1, prove: connect O 1A, O 1B, AB, then: O 1A=O 1B∴ arc O 1A= arc o/kloc-0. ∴∠ADB+∠AO 1B= 180 degrees ≈aO 1b = 2∠c (the circle angle subtended by the same arc is equal to half the central angle) ∴∠ C. It is proved that. ∫acbe * * circle ACD =∠e∠Bao 1 =∠bdo 1 bdo 1+∞。 I used two different methods to solve the two problems, hoping to help you.