用作差法就可以了，具体如下： y/(x-y)-z/(x-z)=xy-yz-xz+zy/(x-y)(x-z)=x(y-z)/(x-y)(x-z) 讨论，因为y-z>0,x-z>0,x-y>0 若x>0,则y/(x-y)-z/(x-z)>0,y/(x-y)>z/(x-z) 若x<0,则y/(x-y)-z/(x-z)<0,y/(x-y)<z/(x-z)