∵∠AOE+∠AOF=180°,∠AOE=40°
∴∠AOF=180°-∠AOE=180°-40°=140°
∵OC平分角AOF
∴∠COF=∠AOF /2=140°/2=70°
又∠COF=∠DOE(对顶角)
∴∠DOE=70°
∵∠AOE+∠BOE=∠AOB=90°
∴∠BOE=90°-∠AOE=90°-40°=50°
∴∠BOD=∠DOE-∠BOE=70°-50°=20°
写出什么因为所以,还有每一步的理由
∵∠AOE+∠AOF=180°,∠AOE=40°
∴∠AOF=180°-∠AOE=180°-40°=140°
∵OC平分角AOF
∴∠COF=∠AOF /2=140°/2=70°
又∠COF=∠DOE(对顶角)
∴∠DOE=70°
∵∠AOE+∠BOE=∠AOB=90°
∴∠BOE=90°-∠AOE=90°-40°=50°
∴∠BOD=∠DOE-∠BOE=70°-50°=20°