∵OC平分∠AOB∠AOB=120°，∴∠AOC＝∠COB＝1／2∠AOB＝60∵OD平分∠BOC∴∠COD＝∠DOB＝1／2∠BOC＝30又∵∠AOD＝∠AOB－∠DOB∴∠AOD=120－30＝90
∵OC平分∠AOB∴∠AOC=∠BOC=60°∵OD平分∠BOC∴∠COD=∠BOD=30°∴∠AOD=∠AOC+∠COD=60°+30°=90°
