this is an expression called 'the difference of 2 squares' since each term is a perfect square. I guess you want to factor it.
in simplest form difference can be written as a^2 - b^2 = (a + b)(a - b)
so if we let a = x - y and b = 2ab we have
(x - y)^2 - 4a^2b^2 = ( x - y + 2ab)(x - y - 2ab)
