①∠COD的余角是∠BOC和∠AOB,∠AOD的补角是∠COD和∠DOE
②∵∠AOC:∠COE=4:5 且∠AOE=180°
∴∠AOC=80° ∠COE=100°
又∵OB平分∠AOC
∴∠AOB=40°