题目

（本题满分8分）如图，AB是⊙O的直径，过B点作⊙O的切线，交弦AE的延长线于点C，作，垂足为D，若，，求DE的长．  答案：解法一：∵BC是⊙O的切线，     ∴．在Rt△ABC中，∵， ∴．∴．··············································································· 3分在Rt△AOD中，， ∴．···· 6分∵，   ∴．··························································· 8分解法二：连接BE．∵AB为直径，∴．∴．∴．·········································· 3分在Rt△ABC中，∵，∴． ∴．························································ 6分∵，         ∴．·················································· 8分解析:略 

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