证明：∵AD平分∠BAC∴∠BAD=∠CAD∵AE=AC,AD=AD∴△ACD≌△AEC （SAS）∴CD＝ED∴∠DEC＝∠DCE∵EF//BC∴∠FEC＝∠DCE∴∠DEC＝∠FEC∴CE平分∠DEF
