（4x+2000)+y=28000 求x y

已知：4x = 5y,求(x+y) ：y |x-y |=x-y |x |=1999 |y |2000,求x+y的值 已知4x=9y求(1)x+y/y (2)y-x/2x 2x-y=2,求[(x²+y²)-(x-y)²+2y(x-y)]÷4y 已知2x-y=10,求[(x²+y²)-(x-y)²+2y(x-y)]/4y 已知x*x-4xy+4y*y=0 求[2x(x+y)-y(x+y)]/(4x*x-4xy+y*y)的值? 已知x/y=2,求2x(x+y)-y(x+y)/4x²-4xy+y² 二元函数f(x,y)=x+y/x-y,求f(y/x,x/y) 求y'=y/(y-x) 已知x=1/3,y=-1/2,求代数式x-(x+y)+(x+2y)-(x+3y)+(x+4y)-(x+5y)+...-( y*y*y*y+2x*x*x*x=4x*x*y 求x等于几,y等于几,写出所有选项! 已知x²+y²+5=2x+4y,求【2x²-(x-y)(x-y)】【(x+y-1)(x-y