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School of Science
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YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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½Â þ~a~bêêêþþþÈÈÈ~a · ~b,=
~a · ~b = |~a ||~b | cos θ,Ù¥§θ~a~b�Y�"
∵ |~b | cos θ = Prja~b , |~a | cos θ = Prjb~a,
∴ ~a · ~b = |~b |Prjb~a = |~a |Prja~b
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YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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½Â þ~a~bêêêþþþÈÈÈ~a · ~b,=
~a · ~b = |~a ||~b | cos θ,Ù¥§θ~a~b�Y�"
∵ |~b | cos θ = Prja~b , |~a | cos θ = Prjb~a,
∴ ~a · ~b = |~b |Prjb~a = |~a |Prja~b
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YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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'uêþÈ�`²1 ~a · ~a = |~a |2
yµ∵ θ = 0,∴ ~a · ~a = |~a ||~a | cos θ = |~a |2
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yµ�þ~a~b�k´"þ§(ؤ
á"e¡y²�~a~bÑ´"þ�/µ
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±cos θ = 0§l
θ =
pi
2
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§XJ~a⊥~b§@oθ = pi
2
§cos θ = 0§u
´~a · ~b = |~a ||~b | cos θ = 0"
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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êþÈÎÜe�$5Ƶ
�Æ ~a · ~b = ~b · ~a,
©�Æ (~a + ~b) · ~c = ~a · ~c + ~b · ~c,
(ÜÆ (λ~a) · ~b = λ(~a · ~b),λê.
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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-êêêþþþÈÈÈ���IIILLLªªª:
�~a = ax~i + ay~j + az~k§~b = bx~i + by~j + bz~k"
UêþÈ�$5Æ�µ
~a · ~b = (ax~i + ay~j + az~k) · (bx~i + by~j + bz~k)
= ax~i · (bx~i + by~j + bz~k) + ay~j · (bx~i + by~j + bz~k)
+az~k · (bx~i + by~j + bz~k)
= axbx~i ·~i + axby~i ·~j + axbz~i · ~k
+aybx~j ·~i + ayby~j ·~j + aybz~j · ~k
+azbx~k ·~i + azby~k ·~j + azbz~k · ~k
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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-êêêþþþÈÈÈ���IIILLLªªª:
�~a = ax~i + ay~j + az~k§~b = bx~i + by~j + bz~k"
UêþÈ�$5Æ�µ
~a · ~b = (ax~i + ay~j + az~k) · (bx~i + by~j + bz~k)
= ax~i · (bx~i + by~j + bz~k) + ay~j · (bx~i + by~j + bz~k)
+az~k · (bx~i + by~j + bz~k)
= axbx~i ·~i + axby~i ·~j + axbz~i · ~k
+aybx~j ·~i + ayby~j ·~j + aybz~j · ~k
+azbx~k ·~i + azby~k ·~j + azbz~k · ~k
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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du~i!~j!~kpR§¤±
~i ·~j =~j · ~k = ~k ·~i = 0;~j ·~i = ~k ·~j =~i · ~k = 0.
qdu~i!~j!~k��þ1§¤±
~i ·~i =~j ·~j = ~k · ~k = 1
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~a · ~b = axbx + ayby + azbz .
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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~i ·~i =~j ·~j = ~k · ~k = 1
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~a · ~b = axbx + ayby + azbz .
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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~i ·~i =~j ·~j = ~k · ~k = 1
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~a · ~b = axbx + ayby + azbz .
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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du~a · ~b = |~a ||~b | cos 觤±�~a!~bÑØ´"þ§k
cos θ =
~a · ~b
|~a ||~b |
±êþÈ�IL«ª=þ���IL«ª\þª§
��üþY�{u�IL«ªµ
cos θ =
axbx + ayby + azbz√
a2x + a
2
y + a
2
z
√
b2x + b
2
y + b
2
z
¤±§~a ⊥ ~b ⇐⇒ axbx + ayby + azbz = 0
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du~a · ~b = |~a ||~b | cos 觤±�~a!~bÑØ´"þ§k
cos θ =
~a · ~b
|~a ||~b |
±êþÈ�IL«ª=þ���IL«ª\þª§
��üþY�{u�IL«ªµ
cos θ =
axbx + ayby + azbz√
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2
y + a
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z
√
b2x + b
2
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z
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YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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cos θ =
~a · ~b
|~a ||~b |
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��üþY�{u�IL«ªµ
cos θ =
axbx + ayby + azbz√
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√
b2x + b
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YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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~1: ®n:M(1, 1, 1)!A(2, 2, 1)!ÚB(2, 1, 2)§
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) þ
−−→
MA9
−−→
MB§∠AMBÒ´§m�Y�"ù
p§l
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MA · −−→MB = 1 × 1+ 1 × 0+ 0 × 1
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12 + 12 + 02 =
√
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√
12 + 02 + 12 =
√
2
\üþY�{u�Lª§��
cos ∠AMB =
−−→
MA · −−→MB
|−−→MA ||−−→MB |
=
1
2
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pi
3
"
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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3 þ�·ÜÈ
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¢~ �Om\L�|:§kå~F^uùm\þP:?©
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−−→
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�
|~M| = |OQ ||~F | = |−−→OP ||~F | sin θ
5µ ~M�Ru
−−→
OP~F¤û½�²¡§ÎÜmÃX"
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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üþ�þÈ
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�
|~M| = |OQ ||~F | = |−−→OP ||~F | sin θ
5µ ~M�Ru
−−→
OP~F¤û½�²¡§ÎÜmÃX"
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üþ�þÈ
½Â þ~a~b�þþþÈÈÈ~c = ~a × ~b
~c��:|~c | = |~a ||~b | sin θ,
θ~a~b�Y�,
5µ ~c�QRu~a§qRu~b§ÎÜmÃX"þÈ
¡µ�È! È
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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üþ�þÈ
½Â þ~a~b�þþþÈÈÈ~c = ~a × ~b
~c��:|~c | = |~a ||~b | sin θ,
θ~a~b�Y�,
5µ ~c�QRu~a§qRu~b§ÎÜmÃX"þÈ
¡µ�È! È
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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þþþ���···ÜÜÜÈÈÈ
üþ�þÈ
'uþÈ�`²1 ~a × ~a = ~0
yµ∵ θ = 0,∴ |~a × ~a | = |~a |2 sin 0 = 0
'uþÈ�`²2 ~a ∥ ~b ⇐⇒ ~a × ~b = ~0
yµ�þ~a~b�k´"þ§(ؤ
á"e¡y²�~a~bÑ´"þ�/µ
XJ~a × ~b = ~0§du|~a | , 0§|~b | , 0§¤
±sin θ = 0§l
θ = 0§=~a ∥ ~b¶
§XJ~a ∥ ~b§@oθ = 0½θ = pi§sin θ = 0§
u´|~a × ~b | = |~a ||~b | sin θ = 0"
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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üüüþþþ���þþþÈÈÈ
þþþ���···ÜÜÜÈÈÈ
üþ�þÈ
þÈÎÜe�$5Ƶ
~a × ~b = −~b × ~a,
©�Æ (~a + ~b) × ~c = ~a × ~c + ~b × ~c,
(ÜÆ (λ~a) × ~b = ~a × (λ~b) = λ(~a × ~b),λê.
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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þþþ���···ÜÜÜÈÈÈ
üþ�þÈ
-þþþÈÈÈ���IIILLLªªª:
�~a = ax~i + ay~j + az~k§~b = bx~i + by~j + bz~k"
UþÈ�$5Æ�µ
~a × ~b = (ax~i + ay~j + az~k) × (bx~i + by~j + bz~k)
= ax~i × (bx~i + by~j + bz~k) + ay~j × (bx~i + by~j + bz~k)
+az~k × (bx~i + by~j + bz~k)
= axbx(~i ×~i) + axby(~i ×~j) + axbz(~i × ~k)
+aybx(~j ×~i) + ayby(~j ×~j) + aybz(~j × ~k)
+azbx(~k ×~i) + azby(~k ×~j) + azbz(~k × ~k)
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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þþþ���···ÜÜÜÈÈÈ
üþ�þÈ
-þþþÈÈÈ���IIILLLªªª:
�~a = ax~i + ay~j + az~k§~b = bx~i + by~j + bz~k"
UþÈ�$5Æ�µ
~a × ~b = (ax~i + ay~j + az~k) × (bx~i + by~j + bz~k)
= ax~i × (bx~i + by~j + bz~k) + ay~j × (bx~i + by~j + bz~k)
+az~k × (bx~i + by~j + bz~k)
= axbx(~i ×~i) + axby(~i ×~j) + axbz(~i × ~k)
+aybx(~j ×~i) + ayby(~j ×~j) + aybz(~j × ~k)
+azbx(~k ×~i) + azby(~k ×~j) + azbz(~k × ~k)
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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þþþ���···ÜÜÜÈÈÈ
üþ�þÈ
du~i!~j!~kpR§¤±
~i ×~i =~j ×~j = ~k × ~k = 0
qk
~i ×~j = ~k ,~j × ~k =~i, ~k ×~i =~j;~j ×~i = −~k , ~k ×~j = −~i,~i × ~k = −~j.
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�üþ�þÈ�IL«ªµ
~a × ~b = (aybz − azby)~i + (azbx − axbz)~j + (axby − aybx)~k .
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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üþ�þÈ
du~i!~j!~kpR§¤±
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qk
~i ×~j = ~k ,~j × ~k =~i, ~k ×~i =~j;~j ×~i = −~k , ~k ×~j = −~i,~i × ~k = −~j.
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�üþ�þÈ�IL«ªµ
~a × ~b = (aybz − azby)~i + (azbx − axbz)~j + (axby − aybx)~k .
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
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üþ�þÈ
du~i!~j!~kpR§¤±
~i ×~i =~j ×~j = ~k × ~k = 0
qk
~i ×~j = ~k ,~j × ~k =~i, ~k ×~i =~j;~j ×~i = −~k , ~k ×~j = −~i,~i × ~k = −~j.
Ï
�üþ�þÈ�IL«ªµ
~a × ~b = (aybz − azby)~i + (azbx − axbz)~j + (axby − aybx)~k .
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
JJJjjj
üüüþþþ���êêêþþþÈÈÈ
üüüþþþ���þþþÈÈÈ
þþþ���···ÜÜÜÈÈÈ
üþ�þÈ
PÁ |^n�1�ª§þÈ�IL«ª±�¤µ
~a × ~b =
∣∣∣∣∣∣∣∣∣
~i ~j ~k
ax ay az
bx by bz
∣∣∣∣∣∣∣∣∣
Ö¿ |~a × ~b |L«±~aÚ~b�>�²1o>/�¡È"
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
JJJjjj
üüüþþþ���êêêþþþÈÈÈ
üüüþþþ���þþþÈÈÈ
þþþ���···ÜÜÜÈÈÈ
üþ�þÈ
PÁ |^n�1�ª§þÈ�IL«ª±�¤µ
~a × ~b =
∣∣∣∣∣∣∣∣∣
~i ~j ~k
ax ay az
bx by bz
∣∣∣∣∣∣∣∣∣
Ö¿ |~a × ~b |L«±~aÚ~b�>�²1o>/�¡È"
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
JJJjjj
üüüþþþ���êêêþþþÈÈÈ
üüüþþþ���þþþÈÈÈ
þþþ���···ÜÜÜÈÈÈ
üþ�þÈ
~2 �~a = (2, 1,−1)§~b = (1,−1, 2)§O~a × ~b"
)
~a × ~b =
∣∣∣∣∣∣∣∣∣
~i ~j ~k
2 1 −1
1 −1 2
∣∣∣∣∣∣∣∣∣ =~i − 5~j − 3~k
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
JJJjjj
üüüþþþ���êêêþþþÈÈÈ
üüüþþþ���þþþÈÈÈ
þþþ���···ÜÜÜÈÈÈ
üþ�þÈ
~3 ®n�/ABC�º:©O
A(1, 2, 3)!B(3, 4, 5)ÚC(2, 4, 7)§
¦n�/ABC�¡È"
) âþÈ�½Â§n�/ABC�¡Èµ
S∆ABC =
1
2
|−−→AB ||−−→AC | sin ∠A = 1
2
|−−→AB × −−→AC |
du
−−→
AB = (2, 2, 2)§
−−→
AC = (1, 2, 4)§Ïd
−−→
AB × −−→AC =
∣∣∣∣∣∣∣∣∣
~i ~j ~k
2 2 2
1 2 4
∣∣∣∣∣∣∣∣∣ = 4~i − 6~j + 2~k
u´S∆ABC =
1
2
|4~i − 6~j + 2~k | = 1
2
√
56 =
√
14
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
JJJjjj
üüüþþþ���êêêþþþÈÈÈ
üüüþþþ���þþþÈÈÈ
þþþ���···ÜÜÜÈÈÈ
µe
1 üþ�êþÈ
2 üþ�þÈ
3 þ�·ÜÈ
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
JJJjjj
üüüþþþ���êêêþþþÈÈÈ
üüüþþþ���þþþÈÈÈ
þþþ���···ÜÜÜÈÈÈ
þ�·ÜÈ
½Â �®nþ~a!~bÚ~c§êþ(~a × ~b) · ~c ¡ùnþ
�·ÜȧP[~a~b~c].
�~a = ax~i + ay~j + az~k§~b = bx~i + by~j + bz~k§
~c = cx~i + cy~j + cz~k"
nþ·ÜÈ�ILªµ
[~a~b~c] = (~a × ~b) · ~c =
∣∣∣∣∣∣∣∣∣
ax ay az
bx by bz
cx cy cz
∣∣∣∣∣∣∣∣∣
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
JJJjjj
üüüþþþ���êêêþþþÈÈÈ
üüüþþþ���þþþÈÈÈ
þþþ���···ÜÜÜÈÈÈ
þ�·ÜÈ
½Â �®nþ~a!~bÚ~c§êþ(~a × ~b) · ~c ¡ùnþ
�·ÜȧP[~a~b~c].
�~a = ax~i + ay~j + az~k§~b = bx~i + by~j + bz~k§
~c = cx~i + cy~j + cz~k"
nþ·ÜÈ�ILªµ
[~a~b~c] = (~a × ~b) · ~c =
∣∣∣∣∣∣∣∣∣
ax ay az
bx by bz
cx cy cz
∣∣∣∣∣∣∣∣∣
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
JJJjjj
üüüþþþ���êêêþþþÈÈÈ
üüüþþþ���þþþÈÈÈ
þþþ���···ÜÜÜÈÈÈ
þ�·ÜÈ
···ÜÜÜÈÈÈ���AAAÛÛÛ¿¿¿Âµ
[~a~b~c] = (~a × ~b) · ~c´ù��
ꧧ�ýéL«±
þ~a!~b!~cc�²18¡N�
NÈ.
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
JJJjjj
üüüþþþ���êêêþþþÈÈÈ
üüüþþþ���þþþÈÈÈ
þþþ���···ÜÜÜÈÈÈ
þ�·ÜÈ
···ÜÜÜÈÈÈ���AAAÛÛÛ¿¿¿ÂÂÂ)))ºººµ
±þ~a!~b!~cc�²18
¡N�.�¡ÈS3êþ�
u|~a × ~b |§§�ph�uþ~c3
þ~a×~bþ�ÝK�ýé§=
h = |Prj~a×~b~c | = |~c || cos θ|
Ù¥§θ´þ~a×~b~c�Y�"
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
JJJjjj
üüüþþþ���êêêþþþÈÈÈ
üüüþþþ���þþþÈÈÈ
þþþ���···ÜÜÜÈÈÈ
þ�·ÜÈ
···ÜÜÜÈÈÈ���AAAÛÛÛ¿¿¿ÂÂÂ)))ºººµ
du[~a~b~c] = (~a × ~b) · ~c
= |~a × ~b ||~c | cos θ
XJþ~a!~b!~c|¤mÃX
£=~c�UmÃ5Kl~a=
~b5(½¤§@o·ÜÈ�Î
Ò´��£θ´b�¤¶
XJþ~a!~b!~c|¤ÃX
£=~c�UÃ5Kl~a=
~b5(½¤§@o·ÜÈ�Î
Ò´K�£θ´ð�¤"
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
JJJjjj
üüüþþþ���êêêþþþÈÈÈ
üüüþþþ���þþþÈÈÈ
þþþ���···ÜÜÜÈÈÈ
þ�·ÜÈ
¤±§²18¡N�Nȵ
V = Sh = |~a × ~b ||~c || cos θ| = |[~a~b~c]|.
nþ~a!~b!~c�¡�¿^´·ÜÈ[~a~b~c] = 0§=∣∣∣∣∣∣∣∣∣
ax ay az
bx by bz
cx cy cz
∣∣∣∣∣∣∣∣∣ = 0
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
JJJjjj
üüüþþþ���êêêþþþÈÈÈ
üüüþþþ���þþþÈÈÈ
þþþ���···ÜÜÜÈÈÈ
þ�·ÜÈ
¤±§²18¡N�Nȵ
V = Sh = |~a × ~b ||~c || cos θ| = |[~a~b~c]|.
nþ~a!~b!~c�¡�¿^´·ÜÈ[~a~b~c] = 0§=∣∣∣∣∣∣∣∣∣
ax ay az
bx by bz
cx cy cz
∣∣∣∣∣∣∣∣∣ = 0
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
JJJjjj
üüüþþþ���êêêþþþÈÈÈ
üüüþþþ���þþþÈÈÈ
þþþ���···ÜÜÜÈÈÈ
þ�·ÜÈ
~4 ®A(1, 2, 0)!B(2, 3, 1)!C(4, 2, 2)!M(x, y, z)o
:�¡§¦:M�Ix, y, z¤÷v�'Xª"
) A(1, 2, 0)!B(2, 3, 1)!C(4, 2, 2)!M(x, y, z)o:�
¡�unþ
−−→
AM,
−−→
AB ,
−−→
AC �¡§ùp
−−→
AM = (x − 1, y − 2, z),−−→AB = (1, 1, 1),−−→AC = (3, 0, 2)
Unþ�¡�¿^�µ∣∣∣∣∣∣∣∣∣
x − 1 y − 2 z
1 1 1
3 0 2
∣∣∣∣∣∣∣∣∣ = 0
=2x + y − 3z − 4 = 0.
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
JJJjjj
üüüþþþ���êêêþþþÈÈÈ
üüüþþþ���þþþÈÈÈ
þþþ���···ÜÜÜÈÈÈ
�
Thank you!
YUAN Peng SS, at ZHBIT 111lllÙÙÙ mmm)))ÛÛÛAAAÛÛÛþþþêêê
两向量的数量积
两向量的向量积
向量的混合积
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