(1)若OC在∠AOB外部,则∠AOC=(3/5)(∠AOB+∠AOC),
∠AOC=(3/2)∠AOB=120°.
(2)若OC在∠AOB内部,则∠AOC=(3/5)(∠AOB-∠AOC),
∠AOC=(3/8)∠AOB=30°.