{(a-b)-x}^2 + {(b-a)-y}^2 = {(a-b)-x}^2 {(a+b)-y}^2
first term of both sides will be cancel out
therefore, {(b-a)-y}^2 = {(a+b)-y}^2
open the term by the formula (a-b)^2 = a^2+b^2-2ab
(b-a)^2 + y^2 -2(b-a)y = (a+b)^2 + y^2+2(a+b)y
y^2 will be cancel out from both sides
now open all the braces
b^2+a^2-2by + 2ay = a^2 + b^2 +2ab +2ay +2by
on solving we get
-2b(a+y) = 2b(b+y)
-(a+y) = (b+y)
-a-b = y-y
therfore. a = -b ANS.