2a(x-y)-3b(y-x)=(x-y)(2a+3b)
a²-2ab+b²-1=(a-b)²-1²=(a-b+1)(a-b-1)
2x²y-8xy+8y=2y(x²-4x+4)=2y(x-2)²
a²（x-y）-4b²(x-y)=(x-y)(a+2b)(a-2b)