问题 解答题
先化简,再求值:
x
x2-1
÷(1+
1
x-1
)
,其中x=2cos30°.
答案

原式=

x
(x+1)(x-1)
÷
x
x-1

=

x
(x+1)(x-1)
×
x-1
x

=

1
x+1

∵x=2×

3
2
=
3

∴原式=

1
3
+1
=
3
-1
2

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