(2/x)+(2/y)=1/2,(5/x)-(1/y)=3/4,求x,y

{6(x-y)-7(x+y)=21 {2(x-y)-5(x+y)=-1 (x-y)/(x+y)=3求( 3x-2y-1)/(x+y-5) x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 {(x+y)/2+(x-y)/3=1,(x+y)-5(x-y)=2.求x=?,y=? 分式的加减:[(x/y-y/x)除以（x+y）+x（1/y-1/x)]除以1+x/y,其中x=5,y=2 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-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) （2x+y-1)(2x-y+1)-(3x+y)(3x-y),其中x=5分之1, 若2x-3y+4=0则x（x*x-1)+x(5-x*x)-6y+7 (x+2y)(x-2y)-(2x-y)的平方+(3x-y)(2x-5y)其中x=-1 y=13分之1 x+y=1 5x-2y=8 3x-y=7 2x-y=3x表示y和用y表示x 解方程组 2x-y=5 2y/x-x/y=12x-y=52y/x-x/y=1 已知x+y=a,2x-y=-2a,求[（x/y-y/x)/(x+y)-x(1/x-1/y)]/[(x+1)/y]的值 若2/x-1/y=3,求[y/x-y/x-y(x-y/x-x+y)]/x-2y/x的值 {x+y=1 ,xy=-6{x(2x-3)=0,y=x²-1{(3x+4y-3)(3x+4y+3)=0,3x+2y=5{(x-y+2)(x+y)=0,x²+y²=8{(x+y)((x+y-1)=0,(x-y)(x-y-1)=0 先化简,再求值[(2x+y)^2-(2x+y)(2x-y)-y(5x+y)]÷(1/2y),其中x-y=2 2y(x+二分之一y)-[(x+y)(x-y)+2y(y+x)],其中|x-1|=2 （x-y)(x+y)-(x+y)^2+2y(y-x),其中x=1,y=3.