三角形两边之和大于第三边

三角形两边之和大于第三边 三角形任意两边的和大于第三边 教学内容:人教版教科书四下第82页例3及“做一做”。 教学目标: 1、探究三角形三边的关系，知道三角形任意两条边的和大于第三边。 2、根据三角形三边的关系解释生活中的现象，提高运用数学知识解决实际问题的能力;提高观察、思考、抽象概括能力和动手操作能力。 3、积极参与探究活动，在活动中获得成功的体验，产生学习的兴趣。 教学重点:知道三角形任意两条边的和大于第三边。 教学难点:对三角形任意两条边的和大于第三边的判断方法。 教具准备:每人准备长1厘米到20厘米，宽5毫米的纸条20张，实验 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 格，课件。 教学过程: 一、创设情境，导入新课 1、故事导入。 师讲述:森林里将要举行一场别开生面的动物舞林大会，这可是酷爱跳舞的红袋鼠盼望已久的事。这一天终于来到了，红袋鼠早早的起床精心打扮了起来，不知不觉时间就过去了很久，红袋鼠终于打扮好了，可一看时间，糟了，舞林大会再过10分钟就要开始了，要来不及了，怎么办呢,这时，妈妈走过来说:“孩子，从我们家出发去舞林大会的会场有很多条路，只要你走那条最近的路，还赶得上参加舞会。”红袋鼠发愁了，这么多路，哪一条最近呢, 出示课件; 游乐园 红袋鼠家 舞林大会的会场 商店 师:这是红袋鼠去会场的路线。请大家仔细观察，它可以怎样走? (从红袋鼠家到会场有三条路线。第一条是先从红袋鼠家到游乐园，再从游乐园到会场;第二条是从红袋鼠家直接到会场;第三条是先从红袋鼠家到商店，再从商店到会场。) 师:在这三条路线中哪条离会场最近? technical department, quality Department, laboratory, measurement and construction team nt implementation of the "quality first, prevention first", a self check and cross-check, check, so that "anyone who was responsible for the construction." 14.2.5 material procurement and management 1, purchase plans according to the construction plan requirements. QC Department to participate in acceptance of materials, negative and seal the incorrect material. 2, according to tender documents and standards for test and evaluation of raw materials, qualified materials classified and piled up and set up a sign detailing acceptance of varieties, quantities, date and signature of management. 14.2.6 nonconforming product control and management of nonconforming products should be controlled on the spot, by construction workers, technicians and QC field fill out the unqualified report, nonconforming should withdraw from the scene and striking identity to avoid misuse. Face treated by supervision engineer's permission to continue construction. 14.2.7 check site laboratory quality supervision and inspection and test management program led by the QC, the test methods, procedures, and strictly according to the contract or a related specification, mainly raw materials and concrete scope of (中间这条最近) 2、探究原因。 师:大家都认为中间这条路线最近，可是你怎么知道这条路线最近呢,把你的想法在小组内和同学们商量一下，也可以结合自己的生活经验谈谈自己的看法。 学生讨论后汇报。 师:( 方案 气瓶 现场处置方案 .pdf气瓶 现场处置方案 .doc见习基地管理方案.doc关于群访事件的化解方案建筑工地扬尘治理专项方案下载 一)同学们都说出了自己的想法，有些同学是结合自己的生活经验谈的，有些同学是用测量的方法量出来的。大家想一想，在生活中这些路线我们不可能去用尺子一米一米地量出它的长短，这个时候我们怎么办, (方案二)同学们都说出了自己的想法，有些同学是结合自己的生活经验谈的，有些同学是用测量的方法量出来的。你的方法与大家不一样，我们看连接红袋鼠家、游乐园、会场三地，近似一个什么图形?连接红袋鼠家、商店、会场三地，同样也近似一个什么图形?那走中间这条路，走过的路程是三角形的一条边，走旁边的路走过的路程实质上是三角形的另两条边的和，你觉得走过的三角形的两条边的和要比第三条边长。那是不是三角形两条边的和都大于第三边呢,(板书:两边之和 第三边)我们来做个实验。 二、小组合作，探究新知 1、实验1:用任意三张纸条摆一个三角形。 (1)(课件出示)实验要求:从准备的学具中任意拿出三张纸条去摆三角形，看看能不能摆成三角形，注意摆的时候端点和端点要连起来，(教师示范)看看你能发现什么, (2)学生动手操作。 (3)全班交流，教师板书。 师:你们有没有摆成三角形，选择的三张纸条分别是几厘米, (4)师小结。 (指黑板)为什么这些可以摆成三角形呢,这些不能摆成三角形呢,下面我们就对这两种情况做一个深入的探究。这里比较多，我们选择上面的三组吧， 2、实验2;深入探究在什么情况下能组成三角形。 (1)动手操作。 ?(课件出示)实验要求:同桌讨论一下，这些能组成三角形的三条边有什么关系，不能组成三角形的三条边有什么关系，也可以借助纸条再摆一摆，然后填写在实验表格中。第一栏写纸条的厘米数，第二栏写比较两边之和与第三边的关系(用算式表示)，最后想一想有什么发现，并写下来。 technical department, quality Department, laboratory, measurement and construction team nt implementation of the "quality first, prevention first", a self check and cross-check, check, so that "anyone who was responsible for the construction." 14.2.5 material procurement and management 1, purchase plans according to the construction plan requirements. QC Department to participate in acceptance of materials, negative and seal the incorrect material. 2, according to tender documents and standards for test and evaluation of raw materials, qualified materials classified and piled up and set up a sign detailing acceptance of varieties, quantities, date and signature of management. 14.2.6 nonconforming product control and management of nonconforming products should be controlled on the spot, by construction workers, technicians and QC field fill out the unqualified report, nonconforming should withdraw from the scene and striking identity to avoid misuse. Face treated by supervision engineer's permission to continue construction. 14.2.7 check site laboratory quality supervision and inspection and test management program led by the QC, the test methods, procedures, and strictly according to the contract or a related specification, mainly raw materials and concrete scope of 出示表格:(单位:厘米) 比较任意两边之和与第三边的关系能摆成三角形的所选纸条 你的发现 (用算式表示) 比较任意两边之和与第三边的关系不能摆成三角形的所选纸条 你的发现 (用算式表示) ?学生动手操作。 ?汇报实验结果。 (2) 分析 定性数据统计分析pdf销售业绩分析模板建筑结构震害分析销售进度分析表京东商城竞争战略分析 、探索。 师:同学们都已经研究好了，谁来汇报一下，你有什么发现。 任意是真么意思,(任意就是不管哪两条边加起来都比第三边要大) ?小结 师:那根据你们的实验观察，大家都认为三角形任意两边之和大于第三边吗, (3)验证结果。 ?师:我们通过实验得出了结论，那是不是所有的三角形都具有这个特征呢,我们来验证一下。你想怎么验证, 学生说。 师:现在就请你用自己喜欢的方法来验证一下。 学生在小组内验证。 ?交流验证结果。 ?小结。 师:同学们通过实验、验证，我们发现如果任意两条线段的和大于第三条线段，这三条线段就能组成三角形，也就是说，三角形的任意两边之和大于第三边。 三、运用新知，解决问题 1、解释红袋鼠选择第二条路线的原因。 师;通过实验，我们知道了三角形三条边的一个规律。现在你能用这个发现来解释红袋鼠家到会场哪条路最近的原因吗,(学生说说) technical department, quality Department, laboratory, measurement and construction team nt implementation of the "quality first, prevention first", a self check and cross-check, check, so that "anyone who was responsible for the construction." 14.2.5 material procurement and management 1, purchase plans according to the construction plan requirements. QC Department to participate in acceptance of materials, negative and seal the incorrect material. 2, according to tender documents and standards for test and evaluation of raw materials, qualified materials classified and piled up and set up a sign detailing acceptance of varieties, quantities, date and signature of management. 14.2.6 nonconforming product control and management of nonconforming products should be controlled on the spot, by construction workers, technicians and QC field fill out the unqualified report, nonconforming should withdraw from the scene and striking identity to avoid misuse. Face treated by supervision engineer's permission to continue construction. 14.2.7 check site laboratory quality supervision and inspection and test management program led by the QC, the test methods, procedures, and strictly according to the contract or a related specification, mainly raw materials and concrete scope of 2、闯红绿灯。 师:红袋鼠在同学们的帮助下，选择了第二条路。可是要顺利到达会场，中间还要经过几个红绿灯。这个红绿灯跟我们生活中的有一些不一样，它只要做对几道题，马上就会亮起绿灯通过去。我们和红袋鼠一起去闯闯吧～ 出示要求:下面每组的三根小棒能组成三角形吗,它会为判断正确的同学亮起绿灯，请你仔细思考哦～ (1) 4 (2) 4 5 4 6 6 (3) 3 (4) 3 3 2 6 6 师:我们每次都是把三条线段中的两条线段相加后才判断的，你们能不能想出一个更简单的方法呢, (用较短的两条线段的和与第三条线段相比较来检验) 3、找朋友。 师:同学们真厉害，和红袋鼠一样顺利的到达了会场，舞林大会马上就要开始了。在舞林大会中比赛，还要找一个朋友，只要完成了下面的题，就可以找到一个朋友一起进行比赛，我们帮红袋鼠想一想。 (课件出示)要求:下面这些线段里面能组成三角形的三条线段是一组好朋友，找找看，哪三条线是一组好朋友,请你写一写，你能找到几组, 3厘米 5厘米 8厘米 10厘米 15厘米 4、师:红袋鼠找到了好朋友，在台上进行了精彩表演，最后获得了冠军。它非常高兴，还要谢谢大家的帮助。 四、反思回顾 师:在这节课里，你有什么收获?学会了什么知识?是怎样学习的? 五、拓展延伸 1、有两根长度分别为2 cm和5 cm的木棒。猜一猜，与它们组成三角形的第三根小棒长几厘米,说说你的想法。 2、你能用下图中的三条线段(分别为4厘米、2厘米、6厘米)围成三角形吗,任意改变一条边使它能组成三角形。 technical department, quality Department, laboratory, measurement and construction team nt implementation of the "quality first, prevention first", a self check and cross-check, check, so that "anyone who was responsible for the construction." 14.2.5 material procurement and management 1, purchase plans according to the construction plan requirements. QC Department to participate in acceptance of materials, negative and seal the incorrect material. 2, according to tender documents and standards for test and evaluation of raw materials, qualified materials classified and piled up and set up a sign detailing acceptance of varieties, quantities, date and signature of management. 14.2.6 nonconforming product control and management of nonconforming products should be controlled on the spot, by construction workers, technicians and QC field fill out the unqualified report, nonconforming should withdraw from the scene and striking identity to avoid misuse. Face treated by supervision engineer's permission to continue construction. 14.2.7 check site laboratory quality supervision and inspection and test management program led by the QC, the test methods, procedures, and strictly according to the contract or a related specification, mainly raw materials and concrete scope of technical department, quality Department, laboratory, measurement and construction team nt implementation of the "quality first, prevention first", a self check and cross-check, check, so that "anyone who was responsible for the construction." 14.2.5 material procurement and management 1, purchase plans according to the construction plan requirements. QC Department to participate in acceptance of materials, negative and seal the incorrect material. 2, according to tender documents and standards for test and evaluation of raw materials, qualified materials classified and piled up and set up a sign detailing acceptance of varieties, quantities, date and signature of management. 14.2.6 nonconforming product control and management of nonconforming products should be controlled on the spot, by construction workers, technicians and QC field fill out the unqualified report, nonconforming should withdraw from the scene and striking identity to avoid misuse. Face treated by supervision engineer's permission to continue construction. 14.2.7 check site laboratory quality supervision and inspection and test management program led by the QC, the test methods, procedures, and strictly according to the contract or a related specification, mainly raw materials and concrete scope of