Question

化简：

y2-x2

x2+2xy+y2

的结果是（　　）

A． x-y x+y

B． x+y x-y

C．- x-y x+y

D．- x+y x-y

Answer 1

y2-x2

x2+2xy+y2

=

(y+x)(y-x)

(x+y)2

=-

x-y

x+y

．
故选C．