摘要： 解:(1)如图4.连结 ······································································ 1分 .······································· 2分 是的直径(也可用勾股定理求得下面的结论) . ················································· 3分 ..········································ 4分 (2)过点 ·········································· 5分 当时. ··········································· 6分 . (也可用勾股定理逆定理证明)······························· 7分 是的切线······················································································· 8分 (3)过点 ···························································· 9分 ························································································· 10分
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在如图所示的平面直角坐标系中，点C在y轴的正半轴上，四边形OABC为平行四边形，OA=2，∠AOC=60°，以OA为直径的⊙P经过点C，交BC于点D，DE⊥AB，交AB于E．