用字母
表
关于同志近三年现实表现材料材料类招标技术评分表图表与交易pdf视力表打印pdf用图表说话 pdf
示数教案
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
第二单元 节能减排
---用字母表示数
信息窗1 用字母表示数
第一课时
一(教学内容:
课本8---9页内容。
二( 教学目标:
1(结合具体情境，了解用字母表示数的意义和作用，学会用字母表示数。
2. 初步学会根据字母所取的值求含有字母的式子的值。
3. 在探究新知识的过程中，感受用字母表示数与现实生活的亲密联系，发展抽象概括能力，简历初步的代数思想。
三、教学重点:
学会用字母表示数及含有字母的式子的值。
四、教学难点:
用字母表示数，由数过渡到字母，形成由具体到抽象的认知过程。
五、教学准备:
ppt
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.
六、教学过程:
(一)口算训练
(二)导入新课
1、师:哪位同学能说说我们生活中还有哪些地方用到字母, (指名回答)
生1:英语课本，学校的名字下面有英文字母。
生2:博习楼A座。
生3:车牌号。
2. 2、观看视频:某班级召开节约能源主题班会。一位男同学说:一个水龙头每分钟可节水10毫升，另一位女同学说:出门时关闭电器开关，平均每个家庭每年可节省50元电费。
问题一:你能从中找出什么问题,你能获得什么信息,
生1: 一个水龙头2分钟 3分钟。。。节水多少毫升。
生2: 每个家庭2年 3年 。。。。能节约多少电费。
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
生3: 我们要爱护我们的能源避免浪费。
时间 (分) 节水量(毫升)
2 2×10=20
3 3×10=30
4 4×10=40
. .
. .
我们用口来表示流水时间，那么口分钟节水量为口×10
如果用?号来表示流水的时间，那么?分钟节水量就是?×10
在数学中，我们经常用字母来表示数。通常用字母t表示时间，t分钟的节水量表示为t×10
(三)新课
师:小明家原来每年的电费是m元，现在每年节省电费150元。节约用电后每年的电费是多少钱,
生:m-150
1、省略乘号，写出下面各式。(课件展示)
?α×χ ?χ×χ ?5×α ?χ×3
?α×b ?α×8 ?b×b ?α×1
如x×3=x?3=3x(数字和字母相乘省略乘号，数字在前字母在后)
(四)、巩固检测
2、书第9页的第一题和第二题
先让学生独立完成，然后交流填写理由。
3、书第10页第5题和第六题。
这是结合实物图巩固用字母表示数的练习。第二组题关系比较复杂，练习时，要引导学生说清图中的意思，再用含有字母的式子表达出结果。
4、书第10页第8题。
这是一道联系实际巩固用字母表示数的练习。练习时，要让学生明白，大坝的高度包括两部分，一部分是水面到坝顶的高度，另一部分是水面以下大坝的高度。
ultra-high and ultra wide strapping should be solid and reliable, should prevent the car unstable objects falling hurts. 4, take the vehicle in a safe place, head, hands and body shall not reveal the compartment to avoid vehicles falls when you start braking. 5, and from the construction site, pitch turning, reversing, when driving in the narrow space should be free of command. 6, the site traffic comes into play to slow down and do it "four-speed", namely: road conditions unknown to slow, bad line slowly, slower start, passing, parking, narrow roads, detours, road bridges, forks road, slow pedestrians crowded locations and access door. 7, and scaffolding near the motorway operation area and other facilities, and barricades shall be set in the road safety labels, safety signs and protective measures, and to ensure that adequate lighting at night. 8, when loading and unloading operation, if the vehicles parked on the ramp, it should be fixed with wedge-shaped pieces of wood on either side of the wheel. 9, the presence of motor vehicles should avoid walking on the right side, and uneven rows of flock to obstruct traffic; avoid vehicle, should not avoid two car intersection, not dead standing next to the parking lot could not back down. 10, motor vehicles towing vehicle with no brakes, traction object objects shall not, shall not enter is between traction and, when traction on ramps, a car and you were allowed to jobs and remain at the bottom. Ten, the prevention of falls from a height, object hit ten basic safety requirements 1, working at height must be neat, do not wear plastic bottom-sliding shoes, high heels, tools should turn into a tool bag. 2, high operating personnel is strictly prohibited to fight each other, so as not to slip in danger of falling. 3, in the climbing operations, structure must be solid and reliable climbing equipment, must be correct. 4, various types of hand-held equipment should be checked before use to ensure safe and secure. Edges of opening job preventing objects falling. 5, construction workers should be provided for channel up and down, do not climb scaffolding, across the balcony, climbing and walking in the non-provided channel. 6, vacant jobs, should have a firm foothold and properly tie off belts field should be configured depending on the circumstances-blocks, railings or other safety devices. 7, when working at height, all items should be stacked smooth, can not be placed in or near the hole, and not interfere with traffic. 8, when demolition work is high, disassembly of the materials, construction waste should be cleaned up and removed in a timely manner, and shall not be any chaos on the walkway placed or dropped down, keep working the aisles clear. 9, when working at height, are not allowed to throw up or down the materials and tools and other objects. 10, the construction site, where a fall may be of any material, should be removed or fixed, demolition work in a restricted area, under supervised
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
5、书第5页第8题。
七、课堂总结:
通过本节课的学习，说说你有什么收获,
八、板书设计:
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
信息窗二《用字母表示数量关系》
教学内容:青岛版义务教育教科书数学四
年级
六年级体育公开课教案九年级家长会课件PPT下载六年级家长会PPT课件一年级上册汉语拼音练习题六年级上册道德与法治课件
下册P12―,15
教学目标:
1、会用字母表示常见的数量关系和
计算公式
六西格玛计算公式下载结构力学静力计算公式下载重复性计算公式下载六西格玛计算公式下载年假计算公式
，并能正确的计算。
2、掌握用字母表示数的简写规则。
3、感受数学语言表达的简洁性，体会数学的价值。
教学重点:使学生会用字母表示常见的数量关系。
教学难点:掌握用字母表示数的简写规则。
教具学具: PPT课件
教学过程:
一、谈话激趣，引入课题:
目前，节能减排，“低碳”环保以及成为了社会发展的新趋势。电动汽车作为新能源汽车，与传统汽车相比，具有清洁、节能、高效、经济等优势。我们一起来欣赏一下吧.
二、探究新知:
1、用含有字母的式子表示数量关系。
提出问题:怎样用一个含有字母的式子表示汽车行驶速度、时间和路程之间的关系,如果t=3，电动汽车行驶了多少千米,
(1)、通常用s表示路程，v表示速度，t表示时间。
(2)、速度×时间=路程
(3)、s=v×t
(4)、对比两个算是，体会用含有字母表示数量关系的简洁性。 ultra-high and ultra wide strapping should be solid and reliable, should prevent the car unstable objects falling hurts. 4, take the vehicle in a safe place, head, hands and body shall not reveal the compartment to avoid vehicles falls when you start braking. 5, and from the construction site, pitch turning, reversing, when driving in the narrow space should be free of command. 6, the site traffic comes into play to slow down and do it "four-speed", namely: road conditions unknown to slow, bad line slowly, slower start, passing, parking, narrow roads, detours, road bridges, forks road, slow pedestrians crowded locations and access door. 7, and scaffolding near the motorway operation area and other facilities, and barricades shall be set in the road safety labels, safety signs and protective measures, and to ensure that adequate lighting at night. 8, when loading and unloading operation, if the vehicles parked on the ramp, it should be fixed with wedge-shaped pieces of wood on either side of the wheel. 9, the presence of motor vehicles should avoid walking on the right side, and uneven rows of flock to obstruct traffic; avoid vehicle, should not avoid two car intersection, not dead standing next to the parking lot could not back down. 10, motor vehicles towing vehicle with no brakes, traction object objects shall not, shall not enter is between traction and, when traction on ramps, a car and you were allowed to jobs and remain at the bottom. Ten, the prevention of falls from a height, object hit ten basic safety requirements 1, working at height must be neat, do not wear plastic bottom-sliding shoes, high heels, tools should turn into a tool bag. 2, high operating personnel is strictly prohibited to fight each other, so as not to slip in danger of falling. 3, in the climbing operations, structure must be solid and reliable climbing equipment, must be correct. 4, various types of hand-held equipment should be checked before use to ensure safe and secure. Edges of opening job preventing objects falling. 5, construction workers should be provided for channel up and down, do not climb scaffolding, across the balcony, climbing and walking in the non-provided channel. 6, vacant jobs, should have a firm foothold and properly tie off belts field should be configured depending on the circumstances-blocks, railings or other safety devices. 7, when working at height, all items should be stacked smooth, can not be placed in or near the hole, and not interfere with traffic. 8, when demolition work is high, disassembly of the materials, construction waste should be cleaned up and removed in a timely manner, and shall not be any chaos on the walkway placed or dropped down, keep working the aisles clear. 9, when working at height, are not allowed to throw up or down the materials and tools and other objects. 10, the construction site, where a fall may be of any material, should be removed or fixed, demolition work in a restricted area, under supervised
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
(5)、如果t=3,电动汽车行驶了多少米,
已知汽车每小时行驶60千米，即v=60,把v=60, t=3,代
入数量关系，求得的s的值就是电动汽车行驶的路程。
s=v×t=60×3=180
答:电动汽车3小时行驶了180千米。
(6)、归纳总结
用含有字母的式子表示数量关系时，首先根据题意写出数量关系
式，再用字母替换对应的量。
2、用含有字母的式子表示计算公式
(1)、如果用C表示周长，用S表示面积，你能用字母表示出正
方形的周长和面积的计算公式吗,
学生独立完成后小组交流 。 a
汇报展示 C=4×a S=a×a a
精讲点拨: 4×a和a×4通常可以写成4?a或者4a;a×a可
以写成a?，读作“a的平方”，表示两个a相乘。
(2)你能用含有字母的式子表示长方形的周长和面积公式吗,
学生独立完成 a
b
三、巩固练习
1、一本笔记本的单价是a元。你会填写下表吗,
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
数量4 7 10 18 25 (本)
总价4 (本) a
2(如果用X表示工作效率，T表示工作时间，C表示工作总量。
那么C=( )，T=( )，X=( )
3.
我每分钟骑v米。
(1)5分钟骑多少米,b分钟骑多少米,
(2)用v表示速度,t表示时间,s表示路程。 S=
(3)如果每分钟行120m，时间是20分钟，路程是多少米,
4(下图是王伯伯家菜园的示意图。
a米
西红柿 黄瓜
b米 a米
(1)用字母表示黄瓜地的面积。当a=20时，黄瓜地的面积是多少平方米,
(2)用字母表示西红柿地的面积。当a=20,b=40时，西红柿地ultra-high and ultra wide strapping should be solid and reliable, should prevent the car unstable objects falling hurts. 4, take the vehicle in a safe place, head, hands and body shall not reveal the compartment to avoid vehicles falls when you start braking. 5, and from the construction site, pitch turning, reversing, when driving in the narrow space should be free of command. 6, the site traffic comes into play to slow down and do it "four-speed", namely: road conditions unknown to slow, bad line slowly, slower start, passing, parking, narrow roads, detours, road bridges, forks road, slow pedestrians crowded locations and access door. 7, and scaffolding near the motorway operation area and other facilities, and barricades shall be set in the road safety labels, safety signs and protective measures, and to ensure that adequate lighting at night. 8, when loading and unloading operation, if the vehicles parked on the ramp, it should be fixed with wedge-shaped pieces of wood on either side of the wheel. 9, the presence of motor vehicles should avoid walking on the right side, and uneven rows of flock to obstruct traffic; avoid vehicle, should not avoid two car intersection, not dead standing next to the parking lot could not back down. 10, motor vehicles towing vehicle with no brakes, traction object objects shall not, shall not enter is between traction and, when traction on ramps, a car and you were allowed to jobs and remain at the bottom. Ten, the prevention of falls from a height, object hit ten basic safety requirements 1, working at height must be neat, do not wear plastic bottom-sliding shoes, high heels, tools should turn into a tool bag. 2, high operating personnel is strictly prohibited to fight each other, so as not to slip in danger of falling. 3, in the climbing operations, structure must be solid and reliable climbing equipment, must be correct. 4, various types of hand-held equipment should be checked before use to ensure safe and secure. Edges of opening job preventing objects falling. 5, construction workers should be provided for channel up and down, do not climb scaffolding, across the balcony, climbing and walking in the non-provided channel. 6, vacant jobs, should have a firm foothold and properly tie off belts field should be configured depending on the circumstances-blocks, railings or other safety devices. 7, when working at height, all items should be stacked smooth, can not be placed in or near the hole, and not interfere with traffic. 8, when demolition work is high, disassembly of the materials, construction waste should be cleaned up and removed in a timely manner, and shall not be any chaos on the walkway placed or dropped down, keep working the aisles clear. 9, when working at height, are not allowed to throw up or down the materials and tools and other objects. 10, the construction site, where a fall may be of any material, should be removed or fixed, demolition work in a restricted area, under supervised
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
的面积是多少平方米,
(3)用字母表示王伯伯家菜地的面积。
四(小结
这节课你有什么收获,
五、板书设计
用字母表示数量关系
速度×时间=路程 正方形的周长和面积公式
s=v×t C=4×a S=a×a
当t=3, v=60时 C=4a S=a?
s=v×t
=60×3 长方形的周长和面积公式
=180 C=(a+b)×2
答:电动汽车3小时 S=ab
行驶了180千米。
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
用字母表示数复习课
教学内容:青岛版四年级数学下册第一单元信息窗
教学目标:
1.通过练习进一步理解用字母表示数的意义，掌握用字母表示数的方法和含有字母的乘法算式的简写、略写的方法，体会用字母表示数的优越性。
2.在具体的生活情境中，能够运用所学知识灵活的写出含有字母的式子并根据已知条件求出含有字母式子的值。
3.通过拓展练习，经历“发现关系—揭示规律—字母表达--拓展交流”的过程，既学会知识，又体验到探究问题的方法。
4.在具体事例中引导学生经历由具体到抽象的过程，培养观察、比较和抽象概括能力。
教学重难点:
重点:理解用字母表示数的意义，能够灵活运用所学知识表示出含有字母的式子并根据已知条件求出含有字母式子的值。
难点:通过解决实际问题，经历“发现关系—揭示规律—字母表达--拓展交流”的过程，学会知识，体验探究问题的方法。
教具、学具:多媒体课件
教学过程:
一、 问题回顾，再现新知。
1.同学们喜欢做游戏吗,今天，我们一起来做个游戏，好不好,
小游戏: “数”
出示课件: 只， 张嘴， 只眼睛， 条腿扑通„„跳下水。
开始: 1 只， 1张嘴， 2 只眼睛， 4 条腿，扑通一声跳下水。
说一说游戏规则，比一比，看一看，你能说到几只。看谁说的只数多。自由说一遍后指名说一说。
讨论:(1)这个儿歌里有一个规律，你能找出来吗, ultra-high and ultra wide strapping should be solid and reliable, should prevent the car unstable objects falling hurts. 4, take the vehicle in a safe place, head, hands and body shall not reveal the compartment to avoid vehicles falls when you start braking. 5, and from the construction site, pitch turning, reversing, when driving in the narrow space should be free of command. 6, the site traffic comes into play to slow down and do it "four-speed", namely: road conditions unknown to slow, bad line slowly, slower start, passing, parking, narrow roads, detours, road bridges, forks road, slow pedestrians crowded locations and access door. 7, and scaffolding near the motorway operation area and other facilities, and barricades shall be set in the road safety labels, safety signs and protective measures, and to ensure that adequate lighting at night. 8, when loading and unloading operation, if the vehicles parked on the ramp, it should be fixed with wedge-shaped pieces of wood on either side of the wheel. 9, the presence of motor vehicles should avoid walking on the right side, and uneven rows of flock to obstruct traffic; avoid vehicle, should not avoid two car intersection, not dead standing next to the parking lot could not back down. 10, motor vehicles towing vehicle with no brakes, traction object objects shall not, shall not enter is between traction and, when traction on ramps, a car and you were allowed to jobs and remain at the bottom. Ten, the prevention of falls from a height, object hit ten basic safety requirements 1, working at height must be neat, do not wear plastic bottom-sliding shoes, high heels, tools should turn into a tool bag. 2, high operating personnel is strictly prohibited to fight each other, so as not to slip in danger of falling. 3, in the climbing operations, structure must be solid and reliable climbing equipment, must be correct. 4, various types of hand-held equipment should be checked before use to ensure safe and secure. Edges of opening job preventing objects falling. 5, construction workers should be provided for channel up and down, do not climb scaffolding, across the balcony, climbing and walking in the non-provided channel. 6, vacant jobs, should have a firm foothold and properly tie off belts field should be configured depending on the circumstances-blocks, railings or other safety devices. 7, when working at height, all items should be stacked smooth, can not be placed in or near the hole, and not interfere with traffic. 8, when demolition work is high, disassembly of the materials, construction waste should be cleaned up and removed in a timely manner, and shall not be any chaos on the walkway placed or dropped down, keep working the aisles clear. 9, when working at height, are not allowed to throw up or down the materials and tools and other objects. 10, the construction site, where a fall may be of any material, should be removed or fixed, demolition work in a restricted area, under supervised
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
(2)小组讨论一下，将你发现的规律想办法表示出来。看谁的办法好。 (学生分组讨论，汇报讨论结果。)
(3)你能用一个字母来说出任意只的儿歌吗,
出示课件:a只，a张嘴，2a只眼睛，4a条腿，扑通一声跳下水
2.前几节课我们一起学习了“用字母表示数”，下面请同学们说一说:你学到了什么,
学生先独立思考回忆，再小组内互相说一说。
找个别学生回答，不完整的其他同学补充。
预设从以下几方面展开:
(1)可以用字母表示题目中的数量。
(2)含有字母的式子里乘号可以记做“.”也可以省略不写。
(3)根据字母的取值，可以求含有字母的式子的值。
小结知识点，摸查学生对用字母表示数的掌握情况，并引入课题。
板书课题:用字母表示数练习
二、分层练习，巩固提高。
(一)基本练习，巩固新知。
1.省略运算符号写出下列各式。
m×8 a×b 15×n x×y x，x
这道题可以先让学生独立完成，再交流做法。重点让学生说出m×8 为什么要写成8m 而不是m8。 x，x要提示学生加号能不能省略，引导学生想到x，x= x×2=2x，强调在含有字母的式子里只有乘号能省略。
2.出示课本第6页第9题
?想一想m和n各表示什么,
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
?试着独立解释每个式子表示的意义并交流订正。
(二)综合练习，应用新知。
1.开动脑筋填一填。
?一个正方形，每边长a米。它的周长( )米。
?一辆汽车t小时行了300千米，平均每小时行( )千米。
?李师傅每小时加工40个零件，加工了a小时，一共加工了( )
个。 ?每袋面粉重a千克，每袋大米重b千克，8袋面粉和5袋大米共重
( )千克。
?苏宁公司在5月5日这一天，某品牌的手机十分畅销，上午卖出75部，
下午卖出100部，已知每部手机a元，这一天一共卖出( )元，
上午比下午少卖出( )元。
ultra-high and ultra wide strapping should be solid and reliable, should prevent the car unstable objects falling hurts. 4, take the vehicle in a safe place, head, hands and body shall not reveal the compartment to avoid vehicles falls when you start braking. 5, and from the construction site, pitch turning, reversing, when driving in the narrow space should be free of command. 6, the site traffic comes into play to slow down and do it "four-speed", namely: road conditions unknown to slow, bad line slowly, slower start, passing, parking, narrow roads, detours, road bridges, forks road, slow pedestrians crowded locations and access door. 7, and scaffolding near the motorway operation area and other facilities, and barricades shall be set in the road safety labels, safety signs and protective measures, and to ensure that adequate lighting at night. 8, when loading and unloading operation, if the vehicles parked on the ramp, it should be fixed with wedge-shaped pieces of wood on either side of the wheel. 9, the presence of motor vehicles should avoid walking on the right side, and uneven rows of flock to obstruct traffic; avoid vehicle, should not avoid two car intersection, not dead standing next to the parking lot could not back down. 10, motor vehicles towing vehicle with no brakes, traction object objects shall not, shall not enter is between traction and, when traction on ramps, a car and you were allowed to jobs and remain at the bottom. Ten, the prevention of falls from a height, object hit ten basic safety requirements 1, working at height must be neat, do not wear plastic bottom-sliding shoes, high heels, tools should turn into a tool bag. 2, high operating personnel is strictly prohibited to fight each other, so as not to slip in danger of falling. 3, in the climbing operations, structure must be solid and reliable climbing equipment, must be correct. 4, various types of hand-held equipment should be checked before use to ensure safe and secure. Edges of opening job preventing objects falling. 5, construction workers should be provided for channel up and down, do not climb scaffolding, across the balcony, climbing and walking in the non-provided channel. 6, vacant jobs, should have a firm foothold and properly tie off belts field should be configured depending on the circumstances-blocks, railings or other safety devices. 7, when working at height, all items should be stacked smooth, can not be placed in or near the hole, and not interfere with traffic. 8, when demolition work is high, disassembly of the materials, construction waste should be cleaned up and removed in a timely manner, and shall not be any chaos on the walkway placed or dropped down, keep working the aisles clear. 9, when working at height, are not allowed to throw up or down the materials and tools and other objects. 10, the construction site, where a fall may be of any material, should be removed or fixed, demolition work in a restricted area, under supervised
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
练习课
一、填空:
1、学校有图书4000本，又买来a本，现在一共有( )本。
2、学校有学生人，其中男生,人，女生有( )人。 a
3、李师傅每小时生产,个零件，10小时生产( )个。
4、姐姐今年a岁，比妹妹年龄的2倍少2岁，妹妹今年( )岁。
5、甲数是x，比乙数少,，乙数是( )，甲乙两数之和是( )，两数之差是( )
6、小花今年12岁，比小兰大a岁，小兰今年( )岁。
7、一件上衣54元，一件裤子48元，买b套这样的衣服，要用( )元。
8、一本故事书有a页，小明每天看x页，看了,天，看了( )页，还剩( )页没看。
9、王阿姨买了,千克香蕉和,千克苹果，香蕉每千克4.8元，苹果每千克5.4元，一共花了( )元。
10、学校买来a个足球,每个m元,又买来b个排球,每个n元,一共用去( )元,足球比排球多用( )元.
11、某工厂每月用水a吨,全年用水( )吨
212、2a表示( )或者( )， a表示( ) ，
a，a，a，a，a,( ) a×a×a,( )
13、果园里有苹果树和梨树共45棵,其中梨树有a棵,苹果树比梨树多( )棵.
14、每个足球x元,买4个足球,付出200元,应找回( )元.
15、三个连续自然数,已知中间一个数是m,那么前一个数是( ),后一个数是( ),三数之和是( )
216、当x,5时,x,( ),2x，8,( )。当x,15时,2x,2×4的值是( )。
17、一种商品降价a元后是80元,原价是( )元.
18、长方形周长计算公式用字母表示是( ) to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
19、李师傅每天做m个零件,比张师傅多做8个,两人一天共做( )个。
20、每本练习本x,买了6本,付出10元,应找回( )元.
21、甲数比乙数大5,如果乙数是m,那么甲数是( )。
22、小红付出30元，买本练习本，每本2元，应找回( ) 元(当xx
,10时，应找回( ) 元
23、食堂买来200千克煤,已烧了a天,还剩b千克,平均每天烧了( )
千克.
24、一批货物a吨，第一次运走b吨，第二次运走c吨，还剩下( )
吨(
25、食堂运来200千克煤，烧了a天，还剩下b千克，平均每天烧( )
克(
二、省略乘号写出下面各式。
a×12, ,×,, a×,, x×,×7,
5×a, 2×;×;, 7×a×b, 2×a×,, 三、判断。
2 1、5，x,5x( ) 2、x，x,x( )
2 3、a×3,3a( ) 4、,,,×2( )
5、2a，3,,5a,( ) 6、2a，3a,5a( )
7、5×a×,,5a,( ) 8、a×7，a,8a( )
四、说一说下面每个式子所表示的意义。
(1)、一天中午的气温是32?，下午比中午的气温降低了x?。
32,x表示:,,,,,,,,,,,,,
(2)、五(2)班有40人订阅《少年文艺》杂志，每本单价,元。40,表示:,,
,,,,,,,,
(3)、一个足球单价a元，一个篮球,元。6 a，4,表示:,,,,,,,,,, (4)、张师傅每小时加工x个零件，朱师傅每小时加工15个零件。5x表示:,,,
,,,,,, x,15表示:,,,,,,,,,,,,,,,,。(x,15)×3表示:,
,,,,,,,,,.
五、求下列各式的值。
ultra-high and ultra wide strapping should be solid and reliable, should prevent the car unstable objects falling hurts. 4, take the vehicle in a safe place, head, hands and body shall not reveal the compartment to avoid vehicles falls when you start braking. 5, and from the construction site, pitch turning, reversing, when driving in the narrow space should be free of command. 6, the site traffic comes into play to slow down and do it "four-speed", namely: road conditions unknown to slow, bad line slowly, slower start, passing, parking, narrow roads, detours, road bridges, forks road, slow pedestrians crowded locations and access door. 7, and scaffolding near the motorway operation area and other facilities, and barricades shall be set in the road safety labels, safety signs and protective measures, and to ensure that adequate lighting at night. 8, when loading and unloading operation, if the vehicles parked on the ramp, it should be fixed with wedge-shaped pieces of wood on either side of the wheel. 9, the presence of motor vehicles should avoid walking on the right side, and uneven rows of flock to obstruct traffic; avoid vehicle, should not avoid two car intersection, not dead standing next to the parking lot could not back down. 10, motor vehicles towing vehicle with no brakes, traction object objects shall not, shall not enter is between traction and, when traction on ramps, a car and you were allowed to jobs and remain at the bottom. Ten, the prevention of falls from a height, object hit ten basic safety requirements 1, working at height must be neat, do not wear plastic bottom-sliding shoes, high heels, tools should turn into a tool bag. 2, high operating personnel is strictly prohibited to fight each other, so as not to slip in danger of falling. 3, in the climbing operations, structure must be solid and reliable climbing equipment, must be correct. 4, various types of hand-held equipment should be checked before use to ensure safe and secure. Edges of opening job preventing objects falling. 5, construction workers should be provided for channel up and down, do not climb scaffolding, across the balcony, climbing and walking in the non-provided channel. 6, vacant jobs, should have a firm foothold and properly tie off belts field should be configured depending on the circumstances-blocks, railings or other safety devices. 7, when working at height, all items should be stacked smooth, can not be placed in or near the hole, and not interfere with traffic. 8, when demolition work is high, disassembly of the materials, construction waste should be cleaned up and removed in a timely manner, and shall not be any chaos on the walkway placed or dropped down, keep working the aisles clear. 9, when working at height, are not allowed to throw up or down the materials and tools and other objects. 10, the construction site, where a fall may be of any material, should be removed or fixed, demolition work in a restricted area, under supervised
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,1、已知a,18，,,25求4 a，2,的值
2、已知x,5，,,13 求3,,4x的值
3、速生杨的树径每年大约增长3厘米。
(1)如果栽种时的树径为5厘米 ，年后这棵树的树径是多少厘米, x
(2)当x=6时，这棵树的树径是多少厘米,
to clean and repair, it is strictly forbidden to head reaches into the mechanical stroke range. 17th article: in overhead transmission line following work should blackout, cannot blackout Shi, due isolation protection measures, crane shall not in overhead transmission line following work, through overhead transmission line should will lifting arm falls, in overhead line side work Shi, regardless of in any situation Xia, lifting arm, and rope or weights, and overhead transmission line of recently distance should not is less than Xia table provides: transmission line voltage 1000 v following 1-15 kV 20-40 kV 60-110 kV 220,000 v Allow minimum distances with the transmission line (m) vertical 1.5 level 1 1.5 2 3 4 5 6 4 6 18th: lamp voltage may not exceed 36 volts, when working in a damp place or metal containers, lamp voltage may not exceed 12 volts. 19th: pressure vessel should have a safety valve, pressure gauge, and avoid sun exposure, collisions, oxygen cylinders to prevent contaminated oil; of acetylene gas, LPG, must have a safety device to prevent tempering. 20th: x-ray and gamma-ray flaw detector operation area, non-operator, not allowed to enter. Article 21st: corrosion, dust and radioactive and toxic work, protective measures are required, and to carry out regular inspection. Spider-man 22nd section III: Spider-man to regular medical examinations of the medical diagnosis, who suffer from high blood pressure, heart disease, anemia, epilepsy and other discomfort in the Spider-man shall not engage in aerial work. 23rd: Spider-man dressed spirit, banned the wearing of hard bottom and easy slip-on shoe nail. 24th: Spider-man material stack stationary, tools should turn into a tool bag, transfer prohibited throwing of objects. 25th: in case of bad weather (such as wind in the above grade) construction safety, prohibition of the open air, lifting and piling. 26th article: ladder shall not deficiency document, no padded using, ladder cross document spacing to 30 cm suitable, using Shi top to tied prison, bottom should take anti-sliding measures, single ladder and ground angle to 60 degrees suitable, ban II people while in ladder Shang job, as needed received long using, should lashing firm, people Word ladder in end of feet pulled prison, in channel at using ladder, due guardianship or set fence. 27th: no security measures, prohibited in hip joints, supports, trusses of the roof truss cantilever beams, and choose the frame and half fixed widget or job to walk on, Spider-man and the ground ... Nine, ten basic security to prevent vehicle damage claim 1, without legal training of qualified certified personnel not familiar with vehicle performance is not driving a car. 2, should insist on doing defense work, vehicle brake, Horn, steering systems, lighting and other safety components such as poor are not allowed out of the car. 3, dump truck, dump truck car hop is strictly prohibited, prohibited goods mixing, loading of vehicles should not overload,
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