Question

数学题第五题快

Answer 1

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