20道七年級數學化簡求值題

．3ab-4ab+8ab-7ab+ab=______． 4．7x-(5x-5y)-y=______． 5．23a3bc2-15ab2c+8abc-24a3bc2-8abc=______． 6．-7x2+6x+13x2-4x-5x2=______． 7．2y+(-2y+5)-(3y+2)＝______． 11．(2x2-3xy+4y2)+(x2+2xy-3y2)=______． 12．2a-(3a-2b+2)+(3a-4b-1)=______． 13．-6x2-7x2+15x2-2x2＝______． 14．2x-(x+3y)-(-x-y)-(x-y)＝______． 16．2x+2y-[3x-2(x-y)]=______． 17．5-(1-x)-1-(x-1)=______． 18．( )+(4xy+7x2-y2)=10x2-xy． 19．(4xy2-2x2y)-( )=x3-2x2y+4xy2+y3． 21．已知A=x3-2x2+x-4，B=2x3-5x+3，計算A+B=______． 22．已知A=x3-2x2+x-4，B=2x3-5x+3，計算A-B=______． 23．若a=-0.2，b=0.5，代數式-(|a2b|-|ab2|)的值為______． 25．一個多項式減去3m4-m3-2m+5得-2m4-3m3-2m2-1，那麼這個多項式等於______． 26．-(2x2-y2)-[2y2-(x2+2xy)]=______． 27．若-3a3b2與5ax-1by+2是同類項，則x=______，y=______． 28．(-y+6+3y4-y3)-(2y2-3y3+y4-7)＝______． 29．化簡代數式4x2-[7x2-5x-3(1-2x+x2)]的結果是______． 30．2a-b2+c-d3=2a+( )-d3=2a-d3-( )=c-( )． 31．3a-(2a-3b)+3(a-2b)-b=______． 32．化簡代數式x-[y-2x-(x+y)]等於______． 33．[5a2+( )a-7]+[( )a2-4a+( )]=a2+2a+1． 34．3x-[y-(2x+y)]=______． 35．化簡|1-x+y|-|x-y|(其中x＜0，y＞0)等於______． 36．已知x≤y，x+y-|x-y|=______． 37．已知x＜0，y＜0，化簡|x+y|-|5-x-y|=______． 38．4a2n-an-(3an-2a2n)＝______． 39．若一個多項式加上-3x2y+2x2-3xy-4得 2x2y+3xy2-x2+2xy， 則這個多項式為______． 40．-5xm-xm-(-7xm)+(-3xm)=______． 41．當a=-1，b=-2時， [a-(b-c)]-[-b-(-c-a)]＝______． 43．當a=-1，b=1，c=-1時， -[b-2(-5a)]-(-3b+5c)＝______． 44．-2(3x+z)-(-6x)+(-5y+3z)=______． 45．-5an-an+1-(-7an+1)+(-3an)＝______． 46．3a-(2a-4b-6c)+3(-2c+2b)=______． 48．9a2+[7a2-2a-(-a2+3a)]=______． 50．當2y-x=5時，5(x-2y)2-3(-x+2y)-100=______．