题目内容

(满分12分)如图,已知是⊙O的直径,是弦,过点作OD⊥AC于,连结

小题1:(1)求证:
小题2:(2)若,求∠的度数.

小题1:证法一:是⊙O的直径
      ······················· (2分)
    又
      ······················· (4分)
      ······················ (6分)
证法二:是⊙O的直径
      ················ (2分)
     即
    
    又  ······················ (3分)
      ··················· (4分)
      ···················· (5分)
     
小题2:(2)(6分)
解:是⊙O的直径,
      ······················· (3分)
     
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