证明:∵BD、CE都是⊿ABC的高
∴∠ADB=∠AEC=90°
∵∠ABD=180°-∠ADB-∠BAD=90°-∠BAD
∠ACE=180°-∠AEC-∠CAE=90°-∠BAD
∴∠ABD=∠ACE
∵AB=AC
∴∠ABC=∠ACB
∴∠OBC=∠OCB
∴OB=OC
∵AB=AC,OB=OC,AO=AO
∴⊿AOB≌⊿AOC﹙SSS﹚
∴∠BAF=∠CAF
∵AB=AC,∠BAF=∠CAF
∴AF⊥BC
证明:∵BD、CE都是⊿ABC的高
∴∠ADB=∠AEC=90°
∵∠ABD=180°-∠ADB-∠BAD=90°-∠BAD
∠ACE=180°-∠AEC-∠CAE=90°-∠BAD
∴∠ABD=∠ACE
∵AB=AC
∴∠ABC=∠ACB
∴∠OBC=∠OCB
∴OB=OC
∵AB=AC,OB=OC,AO=AO
∴⊿AOB≌⊿AOC﹙SSS﹚
∴∠BAF=∠CAF
∵AB=AC,∠BAF=∠CAF
∴AF⊥BC