1.3ab-4ab+8ab-7ab+ab=______.

2.7x-(5x-5y)-y=______.

3.23a3bc2-15ab2c+8abc-24a3bc2-8abc=______.

4.-7x2+6x+13x2-4x-5x2=______.

5.2y+(-2y+5)-(3y+2)=______.

6.(2x2-3xy+4y2)+(x2+2xy-3y2)=______.

7.2a-(3a-2b+2)+(3a-4b-1)=______.

8.-6x2-7x2+15x2-2x2=______.

9.2x-(x+3y)-(-x-y)-(x-y)=______.

10.2x+2y-[3x-2(x-y)]=______.

11.5-(1-x)-1-(x-1)=______.

12.( )+(4xy+7x2-y2)=10x2-xy.

13.(4xy2-2x2y)-( )=x3-2x2y+4xy2+y3.

14.已知A=x3-2x2+x-4,B=2x3-5x+3,計算A+B=______.

15.已知A=x3-2x2+x-4,B=2x3-5x+3,計算A-B=______.

16.若a=-0.2,b=0.5,代數式-(|a2b|-|ab2|)的值為______.

17.一個多項式減去3m4-m3-2m+5得-2m4-3m3-2m2-1,那麼這個多項式等於______.

18.-(2x2-y2)-[2y2-(x2+2xy)]=______.

19.若-3a3b2與5ax-1by+2是同類項,則x=______,y=______.

20.(-y+6+3y4-y3)-(2y2-3y3+y4-7)=______.