解:OD平分∠AOB,OE平分∠BOC∠DOE=∠DOE+∠BOE=1/2∠AOB+1/2∠BOC =1/2(∠AOB+∠BOC) =1/2(40°+60°) =50°∴ ∠DOE=50°
1/2(40+60)=50