设:x/3=y/4=z/7=kx=3k y=4k z=7kx:y=3k:4k=3:4x:y:z=3k:4k:7k=3:4:7
解:令x=3t,则y=4t,z=7tx:y=(3t):(4t)=3:4x:y:z=(3t):(4t):(7t)=3:4:7