计算（x+y）•x2x2-y2+y2x-y-2x2y-2xy2x2-2xy+y2，正确的结果为（　　）A．x+yB．x-yC．y-xD．x-yx+y

题型：单选题难度：一般来源：武汉

计算（x+y）•

x2

x2-y2

+

y2

x-y

-

2x2y-2xy2

x2-2xy+y2

，正确的结果为（　　）

A．x+y

B．x-y

C．y-x

D． x-y x+y

答案

原式=（x+y）•

x2

(x+y)(x-y)

+

y2

x-y

-

2xy(x-y)

(x-y)2

=

x2

x-y

+

y2

x-y

-

2xy

x-y

=

x2+y2-2xy

x-y

=x-y．
故选B．