Question

已知向量a=(2,4,x)向量b=(2,y,2)若向量a的模等于6且向量a垂直于向量b,求x+y的值

Answer 1

4+16+x^2=36

x^2=16

x=4 x=-4

a垂直b

4+4y+2x=0

x=4 y=-3

x=-4 y=1

x+y=1 or x+y=-3