问题标题:
几道初一数学题急啊化简:5(2x-7y)-3(4x-10y)3a²-[4ab²-5(ab²+5/3a²b)-3/2ab²]-a²b4(x²+2y²)-{(x²-2xy+y²)+[x²-(2xy-2y²)]}2m-{n+[4m-3(m+2n)+6m]-5n}其中m=3/2,n=-45
问题描述:

几道初一数学题急啊

化简:5(2x-7y)-3(4x-10y)

3a²-[4ab²-5(ab²+5/3a²b)-3/2ab²]-a²b

4(x²+2y²)-{(x²-2xy+y²)+[x²-(2xy-2y²)]}

2m-{n+[4m-3(m+2n)+6m]-5n}其中m=3/2,n=-4

5a²b-[2a²b-3(2abc-ac²)-5ac²]其中a=-3b=4c=-1

4x²y-{x²y-[3xy²-2/1(4x²y-8xy²+x²y]}-5xy其中x=-1又1/2y=3/1

已知:A=2x²+3xy-8x+3,B=3x平²-2xy+x-5且3A-2B的值与x无关,求y的值

廖貅武回答:
  一、5(2x-7y)-3(4x-10y)   =10x-35y-12x+30y   =-2x-5y   二、3a²-[4ab²-5(ab²+5/3a²b)-3/2ab²]-a²b   =3a²-4ab²+5ab²+25/3a²b+3/2ab²-a²b   =22/3a²b+5/2ab²+3a²   三、4(x²+2y²)-{(x²-2xy+y²)+[x²-(2xy-2y²)]}   =4x²+8y²-x²+2xy-y²+x²-2xy+2y²   =4x²+8y²   四、2m-{n+[4m-3(m+2n)+6m]-5n}   =2m-n-4m+3m+6n-6m+5n   =-5m+10n   =-5*3/2+10*(-4)   =-95/2   五、5a²b-[2a²b-3(2abc-ac²)-5ac²]   =5a²b-2a²b+6abc-3ac²+5ac²   =3a²b+2ac²+6ab   =3*(-3)²*(4)+2*(-3)*1²+6*(-3)*1   =108-5-18=85   六、4x²y-{x²y-[3xy²-1/2(4x²y-8xy²+x²y]}-5xy   =4x²y-x²y+3xy²-2x²y+4xy²-1/2x²y-5xy   =1/2x²y+7xy²-5xy   =1/2*(-3/2)²*1/3+7*(-3/2)*(1/3)²-5(-3/2)(1/3)   =41/24   七、3A-2B   =3*(2x²+3xy-8x+3)-2*(3x²-2xy+x-5)   =6x²+9xy-24x+6-6x²+4xy-2x+10   =13xy-26x+16中不含x项所以13xy-26x=0   即13y=26   得y=2   这么多题,累死我了
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