设x/3=y/5=z/7=k,则x=3k,y=5k,z=7k,代入(x+z-y)/y和(2x+3y+4z)/(5x-3y+z)中(x+z-y)/y=(3k+7k-5k)/(5k)=5k/(5k)=1(2x+3y+4z)/(5x-3y+z)=(6k+15k+28k)/(15k-15k+7k)=49k/(7k)=7
