（x+y）(x-1)-xy-y^2 怎么因式分解?

(x+y)*(x-1)-x*y-y*y=(x+y)*(x-1)-(x+y)*y=(x+y)*(x-y-1)

=x2-x+xy-y-xy-y2
=x2-x-y-y2
=(x-y)(x+y)-(x+y)
=(x+y)(x-y-1)

=x^2-x+xy-y-xy-y^2
=(x^2-y^2)-(x+y)
=(x+y)(x-y)-(x+y)
=(x+y)(x-y-1)

xx+xy-x-y-xy-yy
=xx-x-y-yy
=(x-y)(x+y)-(x+y)
=(x-y-1)(x+y)

（x+y）(x-1)-xy-y^2
=x^2-x+xy-y-xy-y^2
=(x^2-y^2)-(x+y)
=(x+y)(x-y)-(x+y)
=(x+y)(x-y-1)

（x+y）(x-1)-xy-y^2
=x^2-x+xy-y-xy-y^2
=(x^2-y^2)-(x+y)
=(x+y)(x-y)-(x+y)
=(x+y)(x-y-1)

（x+y）(x-1)-xy-y^2
=（x+y）(x-1)-y(x+y)
=（x+y）(x-y-1)