x+y=15 0.2x+0.5y=4.5 怎么解

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+y=15 0.2x+0.5y=4.5 怎么解 x+y+4.5=12.82x+1.5y=15 15/(X+Y)=0.5 15/(X-Y)=3能得出x+y=30 x-y=5? 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=15y y=x(x 2（x+y)-3(x-y)=3 ,4(x+y)+3(x-y)=15 x^2+y^2=15,x+y=7,x＞y,求x-y x+x+x+x+y+y+y=56 （x+3y)²-2（x-y)（x+y)+(x+y)²其x=0.5,y=-2 x+x+x=15,x+y+y=19,求y-x等于几 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)