解:∵ax6/7=Bx6/5=7/7xC,且abc不为0 ∴等式乘35得:30a=42b=35c ∵42>35>30 ∴b
∵Ax6/7=Bx6/5∴B=5/7A∵Ax6/7=7/7xC∴C=6/7AB