初一代数式求值习题例：3YN+4YN,其中Y=2,N=3要比这难一点,10道

1、3ab-4ab+8ab-7ab+ab=______． a=3,b=2
2．7x-(5x-5y)-y=______． x=2,y=3
3．23a3bc2-15ab2c+8abc-24a3bc2-8abc=______． a=2,b=1,c=3
4．-7x2+6x+13x2-4x-5x2=______． x=2
5．2y+(-2y+5)-(3y+2)＝______． y=-1
6．(2x2-3xy+4y2)+(x2+2xy-3y2)=______． x=-2,y=0
7．2a-(3a-2b+2)+(3a-4b-1)=______．a=-2,b=2
8．-6x2-7x2+15x2-2x2＝______． x=3
9．2x-(x+3y)-(-x-y)-(x-y)＝______． x=y=2
10．2x+2y-[3x-2(x-y)]=______． x=2,y=2
11．5-(1-x)-1-(x-1)=______． x=-2
12．( )+(4xy+7x2-y2)=10x2-xy． x=-2,y=-1
13．(4xy2-2x2y)-( )=x3-2x2y+4xy2+y3． x=-2,y=0
14．已知A=x3-2x2+x-4,B=2x3-5x+3,计算A+B=______．
15．已知A=x3-2x2+x-4,B=2x3-5x+3,计算A-B=______．
16．若a=-0.2,b=0.5,代数式-(|a2b|-|ab2|)的值为______．
17．一个多项式减去3m4-m3-2m+5得-2m4-3m3-2m2-1,那么这个多项式等于______．
18．-(2x2-y2)-[2y2-(x2+2xy)]=______．
19．若-3a3b2与5ax-1by+2是同类项,则x=______,y=______．
20．(-y+6+3y4-y3)-(2y2-3y3+y4-7)＝______．
21．化简代数式4x2-[7x2-5x-3(1-2x+x2)]的结果是______．
22．2a-b2+c-d3=2a+( )-d3=2a-d3-( )=c-( )．
23．3a-(2a-3b)+3(a-2b)-b=______．
24．化简代数式x-[y-2x-(x+y)]等于______．
25．[5a2+( )a-7]+[( )a2-4a+( )]=a2+2a+1．
26．3x-[y-(2x+y)]=______．
27．化简|1-x+y|-|x-y|(其中x＜0,y＞0)等于______．
28．已知x≤y,x+y-|x-y|=______．
29．已知x＜0,y＜0,化简|x+y|-|5-x-y|=______．
30．4a2n-an-(3an-2a2n)＝______．
31．若一个多项式加上-3x2y+2x2-3xy-4得
2x2y+3xy2-x2+2xy,
则这个多项式为______．
32．-5xm-xm-(-7xm)+(-3xm)=______．
33．当a=-1,b=-2时,
[a-(b-c)]-[-b-(-c-a)]＝______．
34．当a=-1,b=1,c=-1时,
-[b-2(-5a)]-(-3b+5c)＝______．
35．-2(3x+z)-(-6x)+(-5y+3z)=______．
36．-5an-an+1-(-7an+1)+(-3an)＝______．
37．3a-(2a-4b-6c)+3(-2c+2b)=______．
38．9a2+[7a2-2a-(-a2+3a)]=______．
39．当2y-x=5时,5(x-2y)2-3(-x+2y)-100=______．

当y=2,n=3时，原式=3*2*3+4*2*3=18+24=42