下列等式中不成立的是（　　）A．xyx2-xy=yx-yB．yx-xy=y2-x2xyC．x2-2xy+y2x-y=x-yD．x2-y2x-y=x-y

题型：单选题难度：简单来源：西城区一模

下列等式中不成立的是（　　）

A． xy x2-xy = y x-y	B． y x - x y = y2-x2 xy
C． x2-2xy+y2 x-y =x-y	D． x2-y2 x-y =x-y

答案

A：原式=

xy

x2-xy

=

xy

x(x-y)

=

y

x-y

，故本答案正确．
B：原式=

y

x

-

x

y

=

y2

xy

-

x2

xy

= 

y2-x2

xy

，故本答案正确．
C：原式=

x2-2xy+y2

x-y

=

(x-y)2

x-y

=x-y，本答案正确．
D：原式=

x2-y2

x-y

=

(x-y)(x+y)

x-y

=x+y，本答案错误．
故选D．