∠AOC+∠BOD-∠DOC=∠AOB
∠AOC+∠BOD=∠AOB+∠DOC
∵∠AOB是∠DOC的3倍
∴∠AOC+∠BOD=∠AOB+(1/3)∠AOB
(4/3)∠AOB=∠AOC+∠BOD=60°+90°=150°
∴∠AOB=150°÷(4/3)=112.5°
∠AOC+∠BOD-∠DOC=∠AOB
∠AOC+∠BOD=∠AOB+∠DOC
∵∠AOB是∠DOC的3倍
∴∠AOC+∠BOD=∠AOB+(1/3)∠AOB
(4/3)∠AOB=∠AOC+∠BOD=60°+90°=150°
∴∠AOB=150°÷(4/3)=112.5°