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