过D作DF‖AE交BC于F
则∠DFB=∠ACB
∵AB=AC
∴∠B=∠ACB
∴∠B=∠DFB
∴DB=DF=CE
∵DF‖AE
∴∠FDP=∠E,∠DFP=∠ECP
∴△DFP≌△ECP (ASA)
∴PD=PE