Question

已知向量a={3,-1,2} ,b={1,2,-1} ,求向量积 a x b,a 点乘 b

Answer 1

a x b
=| i j k
3 -1 2
1 2 -1|
=-3i+5j+7k
a*b
=3×1-1×2-1×2
=-1