a(a-b)³+2a²(b-a)²-2ab(b-a)
=a(a-b)³+2a²(a-b)²+2ab(a-b)
=a(a-b)[(a-b)²+2a(a-b)+2b]
=a(a-b)(a²-2ab+b²+2a²-2ab+2b)
=a(a-b)(3a²-4ab+2b+b²)