原式=2y(x-y)²+4y²(x-y)³
=2y(x-y)²[1+2y(x-y)]
=2y(x-y)²(2xy-2y²+1)
原式=(m-n)³+m(m-n)²-n(m-n)²
=(m-n)²[(m-n)+m-n]
=2(m-n)³