x(x-y)²-2(y-x)³=x(x-y)²＋2(x-y)³=(x-y)²[x+2(x-y)=(x-y)²(x+2x-2y)=(x-y)²(3x-2y)
x(x-y)^2-2(y-x)^3=x(x-y)^2+2(x-y)^3=(x-y)^2[x+2(x-y)]=(x-y)^2(3x-2y)
