题目内容
计算(1)先化简,再求值:x2-4x |
x2-8x+16 |
(2)化简
1 |
x+1 |
2x+1 |
1-x2 |
分析:(1)中先把分子和分母因式分解,然后约分,化成最简分式,再代入x的值求解.
(2)先确定最简公分母,进行通分,然后约分,即可化成最简形式.
(2)先确定最简公分母,进行通分,然后约分,即可化成最简形式.
解答:解:(1)
=
=
当x=5时,原式=5;
(2)
-
=
=
x2-4x |
x2-8x+16 |
x(x-4) |
(x-4)2 |
x |
x-4 |
当x=5时,原式=5;
(2)
1 |
x+1 |
2x+1 |
1-x2 |
=
-3x |
1-x2 |
=
3x |
x2-1 |
点评:本题主要考查分式的化简求值,把分式化到最简是解答的关键,通分、因式分解和约分是基本环节.
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