第一项x/(xy+x+1)=xz/(xyz+xz+z)=xz/(xz+z+1)=xyz/(xyz+yz+y)=1/(yz+y+1)第二项不变第三项z/(zx+z+1)=yz/(xyz+yz+y)=yz/(yz+y+1)再加起来就会发现原式=(yz+y+1)/(yz+y+1)=1
