(2x-y)^2(2x+y)^2=[(2x-y)(2x+y)]^2=[(2x)^2-y^2]^2=[4x^2-y^2]^2=(4x^2)^2-2(4x^2)y^2+(y^2)^2=16x^4-8x^2y^2+y^4
