第四节 因式分解与分式
1.(2016自贡中考)把a 2
-4a 多项式分解因式,结果正确的是( A ) A .a(a -4) B .(a +2)(a -2)
C .a(a +2)(a -2)
D .(a -2)2-4
2.(2016聊城中考)把8a 3-8a 2
+2a 进行因式分解,结果正确的是( C ) A .2a(4a 2-4a +1) B .8a 2(a -1)
C .2a(2a -1)2
D .2a(2a +1)2
3.(2016滨州中考)把多项式x 2
+ax +b 分解因式得(x +1)(x -3),则a ,b 的值分别是( B ) A .a =2,b =3 B .a =-2,b =-3
C .a =-2,b =3
D .a =2,b =-3
4.(2016原创)分式x +y xy 中的字母x ,y 的值都扩大为原来的3倍,则分式的值( A )
A .扩大为原来的3倍
B .缩小为原来的3倍
C .扩大为原来的9倍
D .值不变
5.(2016台州中考)化简(y -x )2x2-y2的结果是( D )
A .-1
B .1
C .y -x x +y
D .x -y x +y
6.(2016河北中考)下列运算结果为x -1的是( B ) A .1-x 1 B .x x2-1·x +1x
C .x x +1÷x -11
D .x +1x2+2x +1
7.(2016北京中考)如果a +b =2,那么代数式a b2·a -b a 的值是( A )
A .2
B .-2
C .21
D .-21
8.(2016安徽中考)因式分解:a 3-a =__a(a +1)(a -1)__.
9.(2016孝感中考)分解因式:2x 2-8y 2=__2(x +2y)(x -2y)__.
10.(2016宜宾中考)分解因式:ab 4-4ab 3+4ab 2=__ab 2(b -2)2__.
11.(2016株洲中考)分解因式:(x -8)(x +2)+6x =__(x +4)(x -4)__.
12.(2016雅安中考)已知a +b =8,a 2b 2=4,则2a2+b2-ab =__28或36__.
13.(2016宿迁中考)计算:x -1x2-x -1x =__x__.
14.(2016扬州中考)当a =2 016时,分式a -2a2-4的值是__2__018__.
15.(2016毕节中考)若a 2+5ab -b 2=0,则a b -b a 的值为__5__.
16.(2016咸宁中考)a ,b 互为倒数,代数式a +b a2+2ab +b2÷(a 1+b 1)的值为__1__.
17.(2016黄石中考)先化简,再求值:a2+a a2-3a ÷a2-1a -3·a -1a +1,其中a =2 016.
解:原式=a (a +1)a (a -3)·a -3(a +1)(a -1)·a -1a +1=a +1.当a =2 016时,原式=2 016+1=2 017.
18.(2016呼和浩特中考)先化简,再求值:
x +11-x2-6x +93-x ÷x -3x2+x ,其中x =-23.
解:原式=x +11-(x -3)23-x ·x (x +1)x -3=x +11+x (x +1)1=x (x +1)x +1=x 1.当x =-23时,原式=23=-32.
19.(2016常德中考)先化简,再求值:
(x2-1x2+x -1-x 1)÷(x -1x2+3x -1),其中x =2.
解:原式=x -11÷x -1x -1=x -1x +1·(x +1)2x -1=x +11.当x =2时,原式=2+11=31.
20.(2016雅安中考)先化简,再求值:
(x2-2x +1x2-1-x -1)÷x -1x +1,其中x =-2.
解:原式=-(x +1)(x +1)(x -1)×x +1x -1=1-(x -1)=2-x.当x =-2时,原式=2-(-2)=4.
21.(2016乐山中考)先化简,再求值:(x -x +13x )÷x2+2x +1x -2,其中x 满足x 2+x -2=0.
解:原式=x +1x (x +1)-3x ·x -2(x +1)2=x +1x (x -2)·x -2(x +1)2=x(x +1)=x 2+x.∵x 2+x -2=0,∴x 2+x
=2,∴原式=2.
22.(2016龙岩中考)先化简,再求值:(x +1-x -13)·x -2x -1,其中x =2+.
解:原式=x -1(x +1)(x -1)-3·x -2x -1=x -2x2-1-3=x -2(x +2)(x -2)=x +2,当x =2+时,原式=2++2
=4+.
23.(2016龙东中考)先化简,再求值:(1+x -21)÷x -2x2-2x +1,其中x =4-tan 45°.
解:原式=x -2x -1·(x -1)2x -2=x -11.当x =4-tan 45°=3时,原式=3-11=21.
24.(2016西宁中考)化简:x +12x -x2-12x +4÷x2-2x +1x +2,然后在不等式x ≤2的非负整数解中选择一个适当的
数代入求值.
解:原式=x +12x -(x +1)(x -1)2(x +2)·x +2(x -1)2=x +12x -x +12x -2=x +12x -2x +2=x +12.∵不等式x ≤2的非负整
数解是0,1,2.又∵x -1≠0,∴x≠1,∴当x =0时,原式=2;当x =2时,原式=32.
25.(2016原创)先化简,再求值:(x2-4x +8-x -22)÷x2-4x +4x -4,其中x =tan 60°-2.
解:原式=(x +2)(x -2)2(x +2)·x -4(x -2)2=(x +2)(x -2)x +8-2x -4·x -4(x -2)2=x +22-x .当x =tan 60°-2=-2
时,原式=-2+23-2)=33=33-3.