解说一下算了:已知x-y/x+y=3那么(x+y)/(x-y)就可以腔搭理解为:1/3(x+y)/2(x-y)就等于1/3除以2或升州者说是乘以1/2.=1/伍笑拿6那么:代数式5(x-y)/x+y-(x+y)/2(x-y)=5*3-1/6