如图A,B是单位圆O上的点,且A,B分别在第一,二象限.C是圆与x轴正半轴的交点,△AOB为正三角形.若A点的坐标为(
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131101230139668816567/SYS201311012301396688165016_ST/0.png)
,
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).记∠COA=α.
(Ⅰ)求
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的值;
(Ⅱ)求cos∠COB的值.
考点分析:
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