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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