题目内容
计算:
(1)
÷(a-b)2
(2)
-
•
(3)先化简,再求值:
,其中a=-8,b=
.
(4)计算
-
.
(1)
a2-b2 |
ab |
(2)
x |
x-1 |
x+3 |
x2-1 |
x2+2x+1 |
x+3 |
(3)先化简,再求值:
3a2-ab |
9a2-6ab+b2 |
1 |
2 |
(4)计算
x-2 |
x+2 |
x+2 |
x-2 |
分析:(1)先分解因式,然后利用除以一个数等于乘以这个数的倒数把除法化为乘法运算,约分后得到最简结果即可;
(2)先把分式因式分解,约分计算乘法,再计算同分母分式化简即可;
(3)先把分式因式分解,约分化简后,再代值计算即可;
(4)先把分式进行通分,再化简为最简分式.
(2)先把分式因式分解,约分计算乘法,再计算同分母分式化简即可;
(3)先把分式因式分解,约分化简后,再代值计算即可;
(4)先把分式进行通分,再化简为最简分式.
解答:解:(1)
÷(a-b)2
=
×
=
;
(2)
-
•
=
-
×
=
-
=
=-
;
(3)
=
=
,
当a=-8,b=
时,原式=
=
;
(4)
-
=
=
.
a2-b2 |
ab |
=
(a+b)(a-b) |
ab |
1 |
(a-b)2 |
=
a+b |
ab(a-b) |
(2)
x |
x-1 |
x+3 |
x2-1 |
x2+2x+1 |
x+3 |
=
x |
x-1 |
x+3 |
(x+1)(x-1) |
(x+1)2 |
x+3 |
=
x |
x-1 |
x+1 |
x-1 |
=
x-x-1 |
x-1 |
=-
1 |
x-1 |
(3)
3a2-ab |
9a2-6ab+b2 |
=
a(3a-b) |
(3a-b)2 |
=
a |
3a-b |
当a=-8,b=
1 |
2 |
-8 | ||
-24-
|
16 |
49 |
(4)
x-2 |
x+2 |
x+2 |
x-2 |
=
(x-2)2-(x+2)2 |
(x+2)(x-2) |
=
-8x |
(x+2)(x-2) |
点评:此题考查了分式的混合运算和分式的化简求值,解答此题的关键是把分式化到最简,然后代值计算.同时注意约分的前提是把各项分子分母中多项式分解因式,化为积的形式,方可约分.
练习册系列答案
相关题目