=xy-y+x-1+y^2-1=y(x-1)+x-1+(y+1)(y-1）=（x-1）*(y+1)+(y+1)*(y-1)=(y+1)*(x+y-2)
题2
=x^3-1+x-1=(x-1)*(x^2+x+1)+x-1=(x-1)*(x^2+x+2)备注：x^3-y^3=(x-y)(x^2+xy+y^2)