∠COE=∠COD+∠DOE
=1/2∠AOD+1/3∠BOD
=1/2(180°-∠BOD)+1/3∠BOD
=90°-1/6∠BOD
=72°
计算得;∠BOD=108°
∠DOE=1/3∠BOD=36°
∠EOB=∠BOD-∠DOE=72°