Because A and B are unitary, (A+B) = 0, if a factor is zero, then its product must be zero.

The meaning of this question is unclear, and there are several ambiguities as follows:

( 1) (a+b) × x/y-xy = 0-xy =-xy

(2) (a+b) × [(x/y)-xy] = 0

(3) (a+b) × {[(x/y)-x]} = 0

(4) (a+b) × [(x-xy) y]/y = 0× (xy-xy？ )=0

Good luck, goodbye.