Question

10．若向量a={-2,3,8},b={-3,4,5},求向量的数量积(a-b)(a+b)

Answer 1

(a-b)=((-2)-(-3),3-4,8-5)=(1,-1,3)

(a+b)=((-2)+(-3),3+4,8+5)=(-5,7,13)

(a-b)(a+b)=1*(-5)+(-1)*7+3*13=27