※ 引述《kyo0010 (~KYO~)》之銘言：
: http://ppt.cc/8EoV
: 如圖的二小題 是向量還是矩陣 小弟還分不太清楚
: 這兩小題也不知道要什麼方法算
: 希望有大大可以給小弟詳解一下
a = (2,1,3), b = (3,-1,2), c = (4,2,-1)
a | 2 1 3 |
(1) a‧(b X c) = det ([ b ]) = | 3 -1 2 | = 35
c | 4 2 -1 |
| i j k |
或者 b X c = | 3 -1 2 | = (-3,11,10)
| 4 2 -1 |
a‧(b X c) = (2,1,3)‧(-3,11,10) = 35
(2) (a X b) X c = -(c‧b)a + (c‧a)b
= -8a + 7b = (5,-15,-10)
| i j k |
或者 a X b = | 2 1 3 | = (5,5,-5)
| 3 -1 2 |
| i j k |
(a X b) X c = | 5 5 -5 | = (5,-15,-10)
| 4 2 -1 |
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