1 . 选修4-1:几何证明选讲
如图,已知
与圆
相切,
为切点,
为割线,弦
,
相交于
点,
为
上一点,且
.
![](https://img.xkw.com/dksih/QBM/2016/9/12/1573014847234048/1573014853287936/STEM/7a652be337cc4d25a7aab4a6d67b6a64.png)
(1)求证:
四点共圆;
(2)若
,
,求
的长.
如图,已知
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bd33764ff4efddfe11a98a609753715c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1dde8112e8eb968fd042418dd632759e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e7b7c83470489253394bd288d7c920df.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a41bcbf7a137218daf88f1deddd2adc0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6d93949d8a15aca4e79cedb978590571.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a0ed1ec316bc54c37c4286c208f55667.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4eedae8d316c76e3d0b451256de03fb9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/994e2fc5676a42e4edba54a291236d7c.png)
![](https://img.xkw.com/dksih/QBM/2016/9/12/1573014847234048/1573014853287936/STEM/7a652be337cc4d25a7aab4a6d67b6a64.png)
(1)求证:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/21a511ffe1a6617f45c48748a16372cd.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1a5a0689f27f06ebd8468e4a5cbab799.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/034a9d2e093d0040c609450c3a344cca.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bd33764ff4efddfe11a98a609753715c.png)
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2 . 如图, AB是圆O的直径,G是AB延长线上的一点,GCD是⊙O的割线,过点G作AG的垂线,交直线AC于点E,交直线AD于点F,过点G作圆O的切线,切点为H.
![](https://img.xkw.com/dksih/QBM/2015/6/10/1572121469919232/1572121476079616/STEM/c4815a07cbfd4097b664c0ac78a7a9b2.png?resizew=189)
(1)求证:C,D,E,F四点共圆;
(2)若GH=6,GE=4,求EF的长.
![](https://img.xkw.com/dksih/QBM/2015/6/10/1572121469919232/1572121476079616/STEM/c4815a07cbfd4097b664c0ac78a7a9b2.png?resizew=189)
(1)求证:C,D,E,F四点共圆;
(2)若GH=6,GE=4,求EF的长.
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