∵∠BOC=2∠AOC
∴∠AOB=∠AOC
又∵OD平分∠AOB
∴∠AOD=∠BOD
2∠AOD=∠AOB=∠AOC
且∠COD=∠AOC+∠AOD=3∠AOD
∴∠AOB=2∠AOD=2×6°40′=13°20′