x=51,y=67;求x-y=___.

x=51,y=67;求x-y=___. 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-Y/X+Y=3,求代数式2(x-y)/X+Y-3X+Y/X+Y 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) x+x+x+y=52 y+y+y+x=36求x (x*x+y*y)(x*x+y*y)-(x*x+y*y)=12 求x*x+y*y等于多少 求微分方程y'=x/y+y/x的通解 y=2x*arctan(y/x),求y‘’ 已知：4x = 5y,求(x+y) ：y 若5x+3y=3x+4y=x+2y+6,则x+y=___ |x-y |=x-y |x |=1999 |y |2000,求x+y的值