七年级数学题目,求解答要过程~好的给分值~

计算：
-8m²-[4m-2m²-(3m-2m²-7)]
=-8m²-(4m-2m²-3m+2m²+7)
=-8m²-4m+2m²+3m-2m²-7
=(-8m²+2m²-2m²)-4m-7
=-8m²-4m-7
3x²-[7x-(4x-3)-2x²]
=3x²-(7x-4x+3-2x²)
=3x²-7x+4x-3+2x²
=(3x²+2x²)+(-7x+4x)-3
=5x²-3x-3
1/2(a²-b)+1/3(a-b²)+1/6(a²+b²)
=1/2a²-1/2b+1/3a-1/3b²+1/6a²+1/6b²
=(1/2a²+1/6a²)-1/2b+1/3a+(-1/3b²+1/6b²)
=2/3a²-1/2b+1/3a-1/6b²
5ab²-3[2a²-2(a²b-2ab²)]
=5ab²-3(2a²-2a²b+4ab²)
=5ab²-6a²+6a²b-12ab²
=(5ab²-12ab²)-6a²+6a²b
=-7ab²-6a²+6a²b
先化简,再求值
1/4(-4x²+2x-8)-(1/2x-1),其中x=1/2
=-x²+1/2x-2-1/2x+1
=-x²-1
=-(1/2)²-1
=-1/4-1
=-5/4
(4a²-3a)-(2a²+a-1)+(2-a²+4a),其中a=-2
=4a²-3a-2a²-a+1+2-a²+4a
=(4a²-2a²-a²)+(-3a-a+4a)+(1+2)
=a²+3
=(-2)²+3
=4+3
=7
a-2(2a+b)+3(a-b),其中a=-2
=a-4a-2b+3a-3b
=(a-4a+3a)-(2b+3b)
=-5b
=-5×(-2)
=10
4x²-(2x²+x-1)+(2-x²-3x),其中x=-1/2
=4x²-2x²-x+1+2-x²-3x
=(4x²-2x²-x²)-(x+3x)+(1+2)
=x²-4x+3
=(-1/2)²-4×(-1/2)+3
=1/4+2+3
=21/4
5(3a²b-ab²)-(ab²+3a²b) 其中a=1/2,b=-1
=15a²b-5ab²-ab²-3a²b
=(15a²b-3a²b)-(5ab²+ab²)
=12a²b-6ab²
=12×(1/2)²×(-1)-6×1/2×(-1)²
=12×1/4×(-1)-6×1/2×1
=-3-3
=-6
已知A=4a²+5b,B=-3a²-2b,求2A-B的值,其中a=-2,b=1
2A-B
=2(4a²+5b)-(-3a²-2b)
=8a²+10b+3a²+2b
=11a²+12b
=11×(-2)²+12×1
=11×4+12
=56
已知(x+1)²+|y-1|=0,求2(xy-5xy²)-(3xy²-xy)的值
∵(x+1)²+|y-1|=0
∴x+1=0 且 y-1=0
∴x=-1,y=1
2(xy-5xy²)-(3xy²-xy)
=2xy-10xy²-3xy²+xy
=3xy-13xy²
=3×(-1)×1-13×(-1)×1²
=-3+13
=10
已知 A=x³+2x²y+2y³-1,B=3+y³+2x²y+2x³,若A+B+C=0,求C
A+B+C=0
C=-(A+B)
C=-(x³+2x²y+2y³-1+3+y³+2x²y+2x³)
=-x³-2x²y-2y³+1-3-y³-2x²y-2x³
=-(x³+2x³)-(2x²y+2x²y)-(2y³+y³)+(1-3)
=-3x³-4x²y-3y³-2