题目内容
先化简，(
-
)÷
，然后给x给一个适当的数求值．
| 3x |
| x-1 |
| 2x |
| x+1 |
| x |
| x2-1 |
原式=
×
-
×
=
×
-
×
=3（x+1）-2（x-1）
=3x+3-2x+2
=x+5．
当x=2时，原式=2+5=7．
| 3x |
| x-1 |
| x2-1 |
| x |
| 2x |
| x+1 |
| x2-1 |
| x |
=
| 3x |
| x-1 |
| (x-1)(x+1) |
| x |
| 2x |
| x+1 |
| (x-1)(x+1) |
| x |
=3（x+1）-2（x-1）
=3x+3-2x+2
=x+5．
当x=2时，原式=2+5=7．
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