证明:作OE垂直AB于E,OF垂直AC于F.
又AO平分∠BAC,则:OE=OF;AO=AO,则Rt⊿AOE≌Rt⊿AOF(HL),AE=AF;
同理可证:Rt⊿BOE≌Rt⊿COF(HL),得:EB=FC.
故:AE+EB=AF+FC,即AB=AC.
证明:作OE垂直AB于E,OF垂直AC于F.
又AO平分∠BAC,则:OE=OF;AO=AO,则Rt⊿AOE≌Rt⊿AOF(HL),AE=AF;
同理可证:Rt⊿BOE≌Rt⊿COF(HL),得:EB=FC.
故:AE+EB=AF+FC,即AB=AC.