证明：过点C作CE‖AD交BA的延长线于点E,∵CE‖AD, ∴∠BAD=∠E, ∠DAC=∠ACE,∵AD为角平分线，∴∠BAD=∠DAC, ∴∠E=∠ACE, ∴AE=AC,∵CE‖AD, ∴BA/AE=BD/DC, ∴AB/AC=BD/DC
