1.x²(x-y)+(y-x)
=x²(x-y)-(x-y)
=(x-y)(x²-1)
=(x-y)(x+1)(x-1)；
2.4x²y-12xy+9y
=y(4x²-12x+9)
=y(2x-3)²
3.4(a+b)²-4(a+b)+1
=[2(a+b)-1]²
=(2a+2b-1)²
4.a^4-2a²b²+b^4
=(a²-b²)²
=(a+b)²(a-b)²