证明:延长CE,交BA的延长线于F.
∵∠BEC=∠BEF=90º;BE=BE;∠CBE=∠FBE.
∴⊿BEC≌⊿BEF(ASA),CE=FE,即CF=2CE.
∵∠ABD=∠ACF(均为∠F的余角);
AB=AC;∠BAD=∠CAF=90º.(已知)
∴⊿BAD≌⊿CAF(ASA),BD=CF=2CE.
证明:延长CE,交BA的延长线于F.
∵∠BEC=∠BEF=90º;BE=BE;∠CBE=∠FBE.
∴⊿BEC≌⊿BEF(ASA),CE=FE,即CF=2CE.
∵∠ABD=∠ACF(均为∠F的余角);
AB=AC;∠BAD=∠CAF=90º.(已知)
∴⊿BAD≌⊿CAF(ASA),BD=CF=2CE.