x（x-y）²-y（x-y）
=(x-y)[x(x-y)-y]
=(x-y)(x²-xy-y)
（x-3）³-4x+12
=(x-3)²-4(x-3）
=（x-3)[(x-3)-4]
=(x-3)(x-7)
x²+8x+16
=(x+4)²
（x² +y²）²-4x²y²
=[(x²+y²)+2xy][(x²+y²)-2xy]
=(x+y)²(x-y)²