- 2(x-y)的平方- 3(x-y)+5(y-x)的平方+(y-x)
=-(x-y)^2-3(x-y)+5(x-y)^2-(x-y)
=(-1+5)(x-y)^2-(3+1)(x-y)
=4(x-y)^2-4(x-y)