作业帮20道七年级数学化简求值题比如：当a=-1，b=-2时，[a-(b-c)]-[-b-(-c-a)]＝______．
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![20道七年级数学化简求值题比如：当a=-1，b=-2时，[a-(b-c)]-[-b-(-c-a)]＝______．](/uploads/image/z/357618-66-8.jpg?t=20%E9%81%93%E4%B8%83%E5%B9%B4%E7%BA%A7%E6%95%B0%E5%AD%A6%E5%8C%96%E7%AE%80%E6%B1%82%E5%80%BC%E9%A2%98%E6%AF%94%E5%A6%82%EF%BC%9A%E5%BD%93a%3D-1%EF%BC%8Cb%3D-2%E6%97%B6%EF%BC%8C%5Ba-%28b-c%29%5D-%5B-b-%28-c-a%29%5D%EF%BC%9D______%EF%BC%8E)
20道七年级数学化简求值题比如：当a=-1，b=-2时，[a-(b-c)]-[-b-(-c-a)]＝______．
20道七年级数学化简求值题
比如：当a=-1，b=-2时，
[a-(b-c)]-[-b-(-c-a)]＝______．
20道七年级数学化简求值题比如：当a=-1，b=-2时，[a-(b-c)]-[-b-(-c-a)]＝______．
．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,计算A+B=______．
22．已知A=x3-2x2+x-4,B=2x3-5x+3,计算A-B=______．
23．若a=-0.2,b=0.5,代数式-(|a2b|-|ab2|)的值为______．
25．一个多项式减去3m4-m3-2m+5得-2m4-3m3-2m2-1,那么这个多项式等于______．
26．-(2x2-y2)-[2y2-(x2+2xy)]=______．
27．若-3a3b2与5ax-1by+2是同类项,则x=______,y=______．
28．(-y+6+3y4-y3)-(2y2-3y3+y4-7)＝______．
29．化简代数式4x2-[7x2-5x-3(1-2x+x2)]的结果是______．
30．2a-b2+c-d3=2a+( )-d3=2a-d3-( )=c-( )．
31．3a-(2a-3b)+3(a-2b)-b=______．
32．化简代数式x-[y-2x-(x+y)]等于______．
33．[5a2+( )a-7]+[( )a2-4a+( )]=a2+2a+1．
34．3x-[y-(2x+y)]=______．
35．化简|1-x+y|-|x-y|(其中x＜0,y＞0)等于______．
36．已知x≤y,x+y-|x-y|=______．
37．已知x＜0,y＜0,化简|x+y|-|5-x-y|=______．
38．4a2n-an-(3an-2a2n)＝______．
39．若一个多项式加上-3x2y+2x2-3xy-4得
2x2y+3xy2-x2+2xy,
则这个多项式为______．
40．-5xm-xm-(-7xm)+(-3xm)=______．
41．当a=-1,b=-2时,
[a-(b-c)]-[-b-(-c-a)]＝______．
43．当a=-1,b=1,c=-1时,
-[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．当2y-x=5时,5(x-2y)2-3(-x+2y)-100=______．
、已知A,B是方程x^2+2x-5=0的两个实数根, 求(A^2+2AB+2A)(B^2+2AB+2B)的值.由A,B是方程x^2+2x-5=0的两个实数根得： AB=-5，A+B=-2 A^2+2AB+2A)(B^2+2AB+2B) =AB（A+2B+2）（B+2A+2） =-5（-2+B+2）（-2+A+2） =-5AB =252、1/2(x+y+z)方+1/2(x-y-z)(x-y+z)-z...
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、已知A,B是方程x^2+2x-5=0的两个实数根, 求(A^2+2AB+2A)(B^2+2AB+2B)的值.由A,B是方程x^2+2x-5=0的两个实数根得： AB=-5，A+B=-2 A^2+2AB+2A)(B^2+2AB+2B) =AB（A+2B+2）（B+2A+2） =-5（-2+B+2）（-2+A+2） =-5AB =252、1/2(x+y+z)方+1/2(x-y-z)(x-y+z)-z(x+y),其中x-y=6,xy=21.要详细步骤化简得： 1/2(x+y+z)方+1/2(x-y-z)(x-y+z)-z(x+y)= 1/2[(x+y)方+2z(x+y)+z方]+1/2[(x-y)方-z方]-z(x+y)= 1/2(x+y)方+1/2(x-y)方=x方＋y方 由x-y=6,xy=21得，x方＋y方＝（x-y）方＋2xy＝783、a^2-ab+2b^2=3 求2ab-2a^2-4b^2-7的值2ab-2a^2-4b^2-7 =2(ab-a^2-2b^2)-7 =-2(a^2-ab+2b^2)-7 =(-2)*3-7 =-6-7=-13 4、若A=2x^2+3xy-2x-3,B=-x^2+xy+2,且3A+6B的值与x无关，求y的值 3A+6B=6x^2+9xy-6x-9-6x^2+6xy+12 =15xy-6x+3 =x(15y-6)+3 5、9x+6x^2 -3(x-2/3x^2).其中x=-2 9x+6x² -3(x-2/3x²) =9x+6x²-3x+2x² =8x²+6x =8×(-2)²+6×(-2) =32-12 =20 6、1/4(-4x^2+2x-8)-(1/2x-1),其中x=1/21/4(-4x²+2x-8)-(1/2x-1) =-x²+1/2x-2-1/2x+1 =-x²-1 =-(1/2)²-1 =-1/4-1 =-5/47、3x'y-[2x'y-(2xyz-x'z)-4x'z]-xyz,其中x=-2,y=-3,z=1, :3x'y-[2x'y-(2xyz-x'z)-4x'z]-xyz =3x'y-2x'y+2xyz-x'z+4x'z-xyz =x'y-xyz+3x'z =4*(-3)-2*3*1+3*4*1 =-12-6+12 =-6 8、(5a^2-3b^2)+(a^2+b^2)-(5a^2+3b^2),其中a=-1,b=1 =5a^2-3b^2+a^2+b^2-5a^2-3b^2 =a^2-5b^2 =(-1)^2-5*1^2 =1-5 =-4 9、2(a^2b+ab^2)-2(a^2 b-1)-2ab^2 -2其中a=-2,b=2 =2a^2b+2ab^2-2a^2b+2-2ab^2-2 =0 10、(X-2分之1Y-1)(X-2分之1Y+1)-(X-2分之1Y-1)的平方 其中X=1.7,Y=3.9(先化简再求值) [(X-2分之1Y)-1][(X+2分之1Y)+1]-(X-2分之1Y-1)平方 =(X+2分之1Y)平方-1-(X-2分之1Y)平方+2(X-2分之1Y)-1 =(X+2分之1Y)平方-(X-2分之1Y)平方+2(X-2分之1Y)-2 =2XY+2X-Y-2 =3.9*2.4+1.4 =10.76
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、已知A,B是方程x^2+2x-5=0的两个实数根, 求(A^2+2AB+2A)(B^2+2AB+2B)的值.由A,B是方程x^2+2x-5=0的两个实数根得： AB=-5，A+B=-2 A^2+2AB+2A)(B^2+2AB+2B) =AB（A+2B+2）（B+2A+2） =-5（-2+B+2）（-2+A+2） =-5AB =252、1/2(x+y+z)方+1/2(x-y-z)(x-y+z)-z...
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、已知A,B是方程x^2+2x-5=0的两个实数根, 求(A^2+2AB+2A)(B^2+2AB+2B)的值.由A,B是方程x^2+2x-5=0的两个实数根得： AB=-5，A+B=-2 A^2+2AB+2A)(B^2+2AB+2B) =AB（A+2B+2）（B+2A+2） =-5（-2+B+2）（-2+A+2） =-5AB =252、1/2(x+y+z)方+1/2(x-y-z)(x-y+z)-z(x+y),其中x-y=6,xy=21.要详细步骤化简得： 1/2(x+y+z)方+1/2(x-y-z)(x-y+z)-z(x+y)= 1/2[(x+y)方+2z(x+y)+z方]+1/2[(x-y)方-z方]-z(x+y)= 1/2(x+y)方+1/2(x-y)方=x方＋y方 由x-y=6,xy=21得，x方＋y方＝（x-y）方＋2xy＝783、a^2-ab+2b^2=3 求2ab-2a^2-4b^2-7的值2ab-2a^2-4b^2-7 =2(ab-a^2-2b^2)-7 =-2(a^2-ab+2b^2)-7 =(-2)*3-7 =-6-7=-13 5、9x+6x^2 -3(x-2/3x^2).其中x=-2 9x+6x² -3(x-2/3x²) =9x+6x²-3x+2x² =8x²+6x =8×(-2)²+6×(-2) =32-12 =20 6、1/4(-4x^2+2x-8)-(1/2x-1),其中x=1/21/4(-4x²+2x-8)-(1/2x-1) =-x²+1/2x-2-1/2x+1 =-x²-1 =-(1/2)²-1 =-1/4-1 =-5/47、3x'y-[2x'y-(2xyz-x'z)-4x'z]-xyz,其中x=-2,y=-3,z=1, :3x'y-[2x'y-(2xyz-x'z)-4x'z]-xyz =3x'y-2x'y+2xyz-x'z+4x'z-xyz =x'y-xyz+3x'z =4*(-3)-2*3*1+3*4*1 =-12-6+12 =-6 8、(5a^2-3b^2)+(a^2+b^2)-(5a^2+3b^2),其中a=-1,b=1 =5a^2-3b^2+a^2+b^2-5a^2-3b^2 =a^2-5b^2 =(-1)^2-5*1^2 =1-5 =-4 9、2(a^2b+ab^2)-2(a^2 b-1)-2ab^2 -2其中a=-2,b=2 =2a^2b+2ab^2-2a^2b+2-2ab^2-2 =0 10、(X-2分之1Y-1)(X-2分之1Y+1)-(X-2分之1Y-1)的平方 其中X=1.7,Y=3.9(先化简再求值) [(X-2分之1Y)-1][(X+2分之1Y)+1]-(X-2分之1Y-1)平方 =(X+2分之1Y)平方-1-(X-2分之1Y)平方+2(X-2分之1Y)-1 =(X+2分之1Y)平方-(X-2分之1Y)平方+2(X-2分之1Y)-2 =2XY+2X-Y-2 =3.9*2.4+1.4 =10.76
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