(本小題滿分10分)選修4—1:幾何證明選講
如圖,已知
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與圓
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相切于點

,半徑
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,

交
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于
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點
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,
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(Ⅰ)求證:

;
(Ⅱ)若圓

的半徑為3,

,求
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的長度.
(Ⅰ)證明:連接
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,
∵

,
∴

.…………………………1分
∵

與圓
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相切于點
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,
∴
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.
∴
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.……………………2分
∵

,
∴

.……………………3分
∴

. ……………………4分
又∵

,
∴

.
∴

. ………………………………5分
(Ⅱ)解:假設(shè)

與圓
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相交于點
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,延長

交圓
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于點

.
∵

與圓
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相切于點
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,

是圓

割線,
∴

.……………6分
∵

,

,
∴

.
∴

.………………………………8分
∴由(Ⅰ)知

.
∴

.
在

中,
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∴
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.…………………………10分
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
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是邊長為
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的正方形,以

為圓心,
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為半徑的圓弧與以

為直徑的圓

交于點

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
并延長

交于

點

(1)求證:

是

的中點
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
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
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是線段
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
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
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如圖,直角三角形ABC中,∠B=

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
C=

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
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在邊BC上(
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
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
表示線段
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
內(nèi)接于⊙

,

是直徑,

與
⊙

相切, 切點為

,


, 則
.

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(本小題滿分10分)選修4-1:幾何證明選講

如圖,已知

ABC中的兩條角平分線

和

相交于

,


B=60

,

在

上,且

。
(Ⅰ)證明:

四點共圓;
(Ⅱ)證明:CE平分

DEF。
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為圓
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的切線,
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為切點,
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,圓
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的面積為
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,則
.
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