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如图所示,已知AB为圆O的直径,点D为线段AB上一点,且AD=
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DB,点C为圆O上一点,且BC=
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025124057364291930/SYS201310251240573642919017_ST/1.png)
AC.点P在圆O所在平面上的正投影为点D,PD=DB.
(1)求证:PA⊥CD;
(2)求二面角C-PB-A的余弦值.
考点分析:
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