题目内容

(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.
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
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