(幾何證明選講選做題)如圖,
PA是圓的切線,
A為切點
PBC是圓的割線,且
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,
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1
解:因為利用圓的切割線定理可知,
PA是圓的切線,
A為切點
可以解得為
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(本小題滿分10分)選修4-1:幾何證明選講
如圖所示,已知
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與⊙
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相切,
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為切點,
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為割線,
弦
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,
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、
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相交于
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點,
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為
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上一點,且
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·
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.
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(1)求證:
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;
(2)求證:
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·
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=
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·
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.
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(幾何證明選做題)如圖,圓O是△ABC的外接圓,過點C的切線交AB的延長線于點 D,CD=
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. 以
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的直角邊
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為直徑作圓
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,圓
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與斜邊
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交于
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,過
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作圓
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的切線與
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交于
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,
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="_________"
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自圓
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外一點
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引圓的一條切線
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,切點為
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,
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為
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的中點,過點
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引圓
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的割線交該圓于
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兩點,且
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,
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.
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⑴求證:
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與
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相似;
⑵求
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的大小.
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是圓

的直徑,直線

與圓
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相切于點
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,
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于點
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,若圓
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的面積為
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,
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,則
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的長為
.
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如圖,四邊形
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為直角梯形,
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,
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,
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,又
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,
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,
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,直線
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與直線
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所成角為
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.
(Ⅰ)求證:平面
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平面
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;
(Ⅱ)求
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與平面
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所成角的正弦值.
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