2(x-y)/3-(x+y)/4=-1 (1) 6(x+y)-4(2x-y)=16 (2)

{3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 3分之2(X-Y)-4分之X+Y=-1,6(X+Y)-4(2X-Y)=16 解方程组：2(x-y)/3-x+y/4=-1 ,6(x+y)-4(2x-y)=16 化简[(3x+4y)^2-(2x+y)(2x-y)+(-x+y)(5x-y)]除以-2y,其中x=-1,y=1 已知x=1/3,y=-1/2,求代数式x-(x+y)+(x+2y)-(x+3y)+(x+4y)-(x+5y)+...-( x+y/2+x-y/3=6,4(x+y)-3(x-y)=-20 {(x+y)/2+(x-y)/3=6 4(x+y)-3(x-y)=-20 4(x+y)-3(x-y)=-20,2/x+y+3/x-y=6 已知4x=9y求(1)x+y/y (2)y-x/2x [(2x+y)^2+(y+2x)(y-2x)-2y(4x-y)]/4y,其中x=1/2,y=1/3 先化简,再求值：[(x+y)(x-y)-(x-y)^2+2y(x-3y)]/(-4y),其中x=1,y=-2 一道二元一次方程组!3(x+y)-4(x-y)=4,(x+y)/2+(x-y)/6=1