Question

已知向量a=(2,-1),b=(x,-2) c=(3,y) 若a‖b,(a+b)⊥(b-c),求x+y

Answer 1

x+y= 0,

a‖b,

2*(-2)-(-1)*X=0,

X=4,

(2+X)(X-3)+(-3)*(-2-Y)=0,

Y=-4.

X+Y=4-4=0.