如圖所示,
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是⊙
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的兩條切線,
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是圓上一點,已知
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,則
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=
.
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試題分析:連BO、CO,
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是⊙
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的兩條切線,所以
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,四邊形OBDC內(nèi)角和為
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,
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.又同弧所對的圓周角是圓心角的一半,所以
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=
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.
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如圖,AB是⊙O的直徑,AC是弦,∠BAC的平分線AD交⊙O于點D,DE⊥AC,交AC的延長線于點E,OE交AD于點F.
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=
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如圖,

切⊙

于點
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,割線

經(jīng)過圓心

,弦
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于點
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,
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,

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_______.
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如圖,⊙

的半徑為3,兩條弦
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,
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交于點
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,且
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,
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,
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.
求證:△
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≌△
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.
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如圖,圓
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的割線
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交圓
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于
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、
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兩點,割線
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經(jīng)過圓心.已知
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,
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,
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.則圓
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.
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
是半圓

的直徑,
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是半圓
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上異于
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的點,
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,垂足為
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,
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