（x+y）的3次方+125
=(x+y+5)[(x+y)²-5(x+y)+25]
=(x+y+5)(x²+y²+2xy-5x-5y+25)
a的3次方c-4a平方bc+4ab平方c
=ac(a²-4ab+4b²)
=ac(a-2b)²
xy-1-x+y
=xy+y-1-x
=y(x+1)-(1+x)
=(y-1)(x+1)