x=y+y+y x+y=84 x=189/y

x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 化简 x / y(x+y) - y / x(x+y) = x=y+y+y x+y=84 x=189/y x(x+y)(x-y)-y(y+x)(y-x)=(x-y)( )填空 x+x+y+y+y=21 ,x+x+y+y+y+y+y=27 ,x ,y=? x+x+y+y+y=21 ,x+x+y+y+y+y+y=27 ,x ,y=? y=x(x x+x+x+x+y+y+y=56 x+x+x+y+y=6.4 y+y+y+x+x=7.1 怎么算? 二元函数f(x,y)=x+y/x-y,求f(y/x,x/y) x-y/x+y=(x-y)²/x²-y²（x≠y) （x+y-5)*（x+y-5)+（x-y+3)=0 x*x-y*y 已知:3x-5y=0,求x/y,x-y/y,x-y/x D：y>=x,y y'/y=1/x ：y' +y= cos x y= 微分方程y - 2y' + y = x 求y'=y/(y-x)