题目内容
①先化简
÷
-
,再给x取一个你喜欢的数代入求值.
②先化简再求值(
-
)÷(
-
),其中a=2,b=1.
x2-4 |
x2-4x+4 |
x+2 |
x+1 |
x |
x-2 |
②先化简再求值(
a |
a-b |
a2 |
a2-2ab+b2 |
a |
a+b |
a2 |
a2-b2 |
分析:①先把分式化简,再把数代入,x取-2,-1和2以外的任何数.
②先把括号内的式子通分,再把除法化为乘法,从而把原式进行化简,把a=2,b=1代入原式即可求出答案.
②先把括号内的式子通分,再把除法化为乘法,从而把原式进行化简,把a=2,b=1代入原式即可求出答案.
解答:解:①
÷
-
=
×
-
=
-
=
=-
,
当x=0时,原式=-
=
;
②(
-
)÷(
-
)
=[
-
]÷[
-
]
=
×
=
,
当a=2,b=1时,原式=
=3.
x2-4 |
x2-4x+4 |
x+2 |
x+1 |
x |
x-2 |
=
(x+2)(x-2) |
(x-2)2 |
x+1 |
x+2 |
x |
x-2 |
=
x+1 |
x-2 |
x |
x-2 |
=
x+1-x |
x-2 |
=-
1 |
x-2 |
当x=0时,原式=-
1 |
0-2 |
1 |
2 |
②(
a |
a-b |
a2 |
a2-2ab+b2 |
a |
a+b |
a2 |
a2-b2 |
=[
a(a-b) |
(a-b)2 |
a2 |
(a-b)2 |
a(a-b) |
(a+b)(a-b) |
a2 |
(a+b)(a-b) |
=
-ab |
(a-b)2 |
(a+b)(a-b) |
-ab |
=
a+b |
a-b |
当a=2,b=1时,原式=
2+1 |
2-1 |
点评:本题考查的是分式的化简求值,第①题注意化简后,代入的数不能使分母的值为0.
练习册系列答案
相关题目