Question

ming831

為什麼可以這樣寫

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=(bc)x(ac)-(ca)x(bc)=0

Answer 1

qn

注意算式什麼時候是向量，什麼時候是純量
[ (b·c)a - (c·a)b ]·c
= [(b·c)a]·c - [(c·a)b]·c
= (b·c)(a·c) - (c·a)(b·c)
= 0