题目内容
先化简,再求值(x-1 |
x+1 |
x+1 |
x+2 |
x+3 |
x2-4 |
2 |
分析:先通分,然后进行四则运算,最后将x=
-1代入.
2 |
解答:解:原式=
÷
=
•
=
•
=-
(4分)
把x=
-1代入上式得:
原式=-
=-
=
-1.(5分)
(x-1)(x+2)-(x+1)2 |
(x+1)(x+2) |
x+3 |
(x+2)(x-2) |
=
x2+x-2-(x2+2x+1) |
(x+1)(x+2) |
(x+2)(x-2) |
x+3 |
=
-(x+3) |
(x+1)(x+2) |
(x+2)(x-2) |
x+3 |
=-
x-2 |
x+1 |
把x=
2 |
原式=-
| ||
|
| ||
|
3 |
2 |
2 |
点评:本题考查了分式的化简求值,解答此题的关键是把分式化到最简,然后代值计算.
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