一道数学题

显示全部楼层 · 2009-6-2 22:42:56

第一个方程得出2XY=6Y-3X，X-2Y=-2XY/3[2X+3XY-4Y]/[X-3XY-2Y]=[3XY+2（X-2Y）]/[-3XY+（X-2Y）]=（3XY-4XY/3）/（-3XY-2XY/3）=（3-4/3）/（-3-2/3）=（5/3）/（-11/3）=-5/11...

千问 · 2009-6-2 22:42:56

1/x-1/2y=1/3方程两边同乘2xy得2y-x=2xy/3
x-2y=-2xy/3方程两边同乘4xy得4y-2x=4xy/32x-4y=-4xy/3 (2x+3xy-4y)/(x-3xy-2y)=(-4xy/3+3xy)/-4xy/3-3xy=-5/13有点晚了不一定对哦脑袋不清楚...

千问 · 2009-6-2 22:42:56

1/x-1/2y=1/3,1/2y-1/x=-1/3(2x+3xy-4y)/(x-3xy-2y)=[(2x-6xy-4y)+9xy]/(x-3xy-2y)=2+9xy/(x-3xy-2y)=2+9/(1/y-2/x -3)=2+9/[2(1/2y-1/x)-3]=2+9/[2*(-1/3)-3]=2-9/(11/3)=-5/11...

千问 · 2009-6-2 22:42:56

分子分母同时除以xy则原式=[-4(1/x-1/2y)+3] /[-2(1/x-1/2y)-3]
=(3-4/3)/(-2/3-3)
=-5/11...

千问 · 2009-6-2 22:42:56

(2x+3xy-4y)/(x-3xy-2y)上下除xy=(2/y+3-4/x)/(1/y-3-2/x)=[-4(1/x-1/2y)+3]/[-2(1/x-1/2y)-3]=(-4*1/3+3)/(-2*1/3-3)=(5/3)/(-11/3)=-5/11...