已知,PB = PC ,即：点P到AB和AC的距离相等,
可得：AP平分∠BAC,即：∠PAB = ∠PAC .
在△BDP和△CDP中,PB = PC ,∠BPD = 90°-∠PAB = 90°-∠PAC = ∠CPD ,DP为公共边,
所以,△BDP ≌ △CDP ,可得：∠BDP = ∠CDP .