1 . 如图所示,PA与圆O相切于点A,不过圆心O的割线PCB与直径AE相交于D点.已知∠BPA=30°,AD=2,PC=1,则圆O的半径等于________ .
![](https://img.xkw.com/dksih/QBM/2017/8/14/1758200027602944/1817081830203392/STEM/91b436abd3534b12b4bbcc4893490293.png?resizew=87)
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2 . 如图所示,AB是半圆O的直径,点C在半圆上,CD⊥AB于点D,且AD=3DB,设∠COD=θ,则tan2
=__ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a16d92d3ccdf0ecfaa43eb8ed62ae5a4.png)
![](https://img.xkw.com/dksih/QBM/2017/8/14/1758200027602944/1817081830195200/STEM/027e6e38fed14b0d94131d2fd983e44c.png?resizew=107)
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3 . 如图,在圆的内接四边形
中,
,
,
,
,则![](https://staticzujuan.xkw.com/quesimg/Upload/formula/16ca90e8a784f990c4097eec9219908d.png)
______ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/45acdbac251ca6b76a166c1242e71df9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3b2aabb3232e9ffabad9def25515cbdc.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5489aaa6dc00789fcf126bf2fd744a02.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3f4aca5534bce25acaeb7379deed8f8f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/16ca90e8a784f990c4097eec9219908d.png)
![](https://img.xkw.com/dksih/QBM/2016/10/23/1573090771615744/1573090777505792/STEM/bd093e7f19e146fb9ff6886c52fac9da.png?resizew=122)
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4 . 如上图,EB、EC是⊙O的两条切线,B、C是切点,A、D是⊙O上两点,如果∠E=46°,∠DCF=32°,则∠A的度数是________
![](https://img.xkw.com/dksih/QBM/2011/6/7/1570238435598336/1570238440374272/STEM/5e7c092980854c6290813da476d5c3e1.png?resizew=168)
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