(幾何證明選講選做題)如圖3,
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是圓
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的切線,切點為
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,
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交圓
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于
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、
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兩點,且
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,
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,則
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的長為
.
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.
試題分析:由切線長定理得
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,
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,
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,
設(shè)
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,由弦切角定理可知
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,
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,
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,即
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,
因此
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,由勾股定理得
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,則
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,解得
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.
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