x+y=50,1500x+2100y=90000怎么解 求过程 要详细

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(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 4(x-y)-3(x-y)=9 5(x-y)+2(x-y)=11 y+10x=x+y+9 10y+x=y+10x+27 3(x+y)-2(x-y)=11 4(x+y)+3(x-y)=9 f(x,y)=x*x*x+y*y*y-9xy+27极值 方程组{x+y+z=50,1500x+2100y+2500z方程组是{x+y+z=50,1500x+2100y+2500z=90000 x+x+x+x+y+y+y=56 先化简再求值 x(9x-y)-y(y-x)+(x-y)的平方,其中x=-1,y=2 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