x+y=300 60%x+90%y=210 的二元一次方程的解为多少

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=? 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+x+y=60 .x-y=4 y=x(x {6(x-y)-7(x+y)=21 {2(x-y)-5(x+y)=-1 X+y=20 90x- 80x+60y-50y=260 怎么解 x+x+x+x+y+y+y=56 x+x+x+y+y=21,x+x+x+x+x+y+y=27,求x=?y=? 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 已知x、y、z是正整数,求解下列联立方程 （x-y)(y-z)(z+x)=-90 (x-y)(y+z)(z-x)=42 (x+y)(y-z)(z-x)=-60 推倒公式:(x+y)(x*x-3x+y*y)=x*x*x+y*y*y怎么做.