题目

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

提问时间：2021-03-22

答案

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