2y+xx2-y2+yy2-x2-2xx2-y2．

题型：解答题难度：一般来源：不详

2y+x

x2-y2

+

y

y2-x2

-

2x

x2-y2

．

答案

原式=

2y+x

x2-y2

-

y

x2-y2

-

2x

x2-y2

=

2y+x-y-2x

x2-y2

=

y-x

(x+y)(x-y)

=-

1

x+y

．