(9X+5Y)/(X+Y)=7.5,求X/Y=?

已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 已知：4x = 5y,求(x+y) ：y 已知X.x+y.y-4x+2y+5=0,求4X.X-12X Y+9Y.y的值 已知4x=9y求(1)x+y/y (2)y-x/2x 二元函数f(x,y)=x+y/x-y,求f(y/x,x/y) 求y'=y/(y-x) |x|=3 |y|=5 |x-y|=|x|+|y| 求 X+Y和 X-Y 等于多少 已知x+y=-5,x*x+y*y=19求xy和（x-y)*(x-y)的值 已知X-Y/X+Y=3,求代数式2(x-y)/X+Y-3X+Y/X+Y x+x+x+y=52 y+y+y+x=36求x 若(x*x+y*y)(x*x+y*y)-4x*x*y*y=0,求代数式(x*x+5xy+y*y)/(x*x+2xy+y* 已知x=1/3,y=-1/2,求代数式x-(x+y)+(x+2y)-(x+3y)+(x+4y)-(x+5y)+...-(