(1)∠2=∠AOB-∠AOD
=180°-80°
=100°
∵OE平分∠BOC
∴∠1=二分之一∠BOC=二分之一×80°=40°
∴∠3=180°-∠1-∠2
=180°-40°-100°
=40°
（2）∠AOD=180°-∠2
=180°-100°
=80°
∠4=∠AOD-∠3
=80°-40°
=40°
∴∠3=∠4=40°
∴OF平分∠AOD