化简(x-y/x2-2xy+y2-xy+y2x2-y2)•xy/y-1= _ .

问题描述:

化简(

x-y
x2-2xy+y2
-
xy+y2
x2-y2
)•
xy
y-1
= ___ .

原式=[

x-y
(x-y)2
-
y(x+y)
(x+y)(x-y)
]•
xy
y-1

=(
1
x-y
-
y
x-y
)•
xy
y-1

=
1-y
x-y
xy
y-1

=-
xy
x-y

故答案是:-
xy
x-y