25 - 4x^2 + 4xy - y^2 = 25 - (4x^2 - 4xy + y^2) = 25 - (2x - y)^2 = (5 - (2x - y)) * (5 + (2x - y) = (5 - 2x + y)(5 + 2x - y)
25 - 4x^2 + 4xy - y^2 = 25 - (4x^2 - 4xy + y^2) = 25 - (2x - y)^2 = (5 - (2x - y)) * (5 + (2x - y) = (5 - 2x + y)(5 + 2x - y)