6(x-y)³-3y(y-x)²
=6(x-y)³-3y(x-y)²
=(x-y)²[6(x-y)-3y]
=3(x-y)²(2x-3y)
mn(m-n)-m(n-m)²
=mn(m-n)-m(m-n)²
=(m-n)[mn-m(m-n)]
=m(m-n)(2n-m)