过E点做EM垂直BC于M,
∠ABE=∠CBE,EM⊥BC,EA⊥AB,AE=ME,△ABE≌△MBE,∠AEB=∠MEB
AD⊥BC,EM⊥BC,AD || EM,∠AFE=∠MEB,∠AFE=∠AEB,AE=AF.