试题:
先化简再求值:(x-y-
x2
x+y
)÷(
2y2
x2+2xy+y2
)+
x2-y2
x-y
,其中x≠y且x,y满足(x-y)(x+y-12)=0.

答案:

我来补答
原式=[
(x-y)(x+y)
x+y
-
x2
x+y
2y2
(x-y)2
+
(x+y)(x-y)
x-y
=
-y2
x+y
(x+y)2
2y2
+x+y
=-
x+y
2
+x+y
=
x+y
2

∵x≠y,且(x-y)(x+y+2)=0
∴x+y-12=0
∴x+y=12
∴原式=6
 
 
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