第1个回答 2008-07-24
(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)
第2个回答 2008-07-24
(x+y)(x-1)-xy-y^2
=(x+y)(x-1)-y(x+y)
=(x+y)(x-y-1)
第3个回答 2008-07-24
=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)
第4个回答 2008-07-24
=x2-x+xy-y-xy-y2
=x2-x-y-y2
=(x-y)(x+y)-(x+y)
=(x+y)(x-y-1)
第5个回答 2008-07-24
(x+y)*(x-1)-x*y-y*y=(x+y)*(x-1)-(x+y)*y=(x+y)*(x-y-1)