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 . 如图所示,⊙O是△ABC的外接圆,AD是⊙O的直径,连接CD,若⊙O的半径r=
,AC=2,则cos B的值是( )
![](https://img.xkw.com/dksih/QBM/2017/8/14/1758200027602944/1817081830154240/STEM/c15e7f13ca2b468897843317de4c17b0.png?resizew=84)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a4b8503f4706b8321e4e79a87eadea84.png)
![](https://img.xkw.com/dksih/QBM/2017/8/14/1758200027602944/1817081830154240/STEM/c15e7f13ca2b468897843317de4c17b0.png?resizew=84)
A.![]() | B.![]() |
C.![]() | D.![]() |
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