(- 2A) square by (a-b-ab)=

(- 2A) square by (a-b-ab)=

If a and B are not equal to 0, a = B
Because (- 2A) ^ 2 > 0, so (a-b-ab) = 0
The common factor AB (a-b) = 0
If a and B are not equal to 0, then a = B