问题 解答题
先化简,再求值:
x
x2-1
÷(1+
1
x-1
)
,其中x=2cos30°-(
3
0
答案

x
x2-1
÷(1+
1
x-1
)=
x
x2-1
÷
x-1+1
x-1

=

x
(x+1)(x-1)
×
x-1
x

=

1
x+1

x=2cos30°-(

3
0=2×
3
2
-1=
3
-1

∴当x=

3
-1时,

原式=

1
x+1
=
1
3
-1+1
=
1
3
=
3
3

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