(-5x+2y)2 = (-5x+2y)(-5x+2y)
= (-5x)(-5x) + (-5x)(2y) + (2y)(-5x) + (2y)(2y)
= 25x^2 - 10xy - 10xy + 4y^2
= 25x^2 - 20xy + 4y^2