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扇形的圆心角是72°,半径为20cm,则扇形的面积为 cm2.
扇形的圆心角是72°,半径为20cm,则扇形的面积为 cm2.
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是夹角为60°的两个单位向量,则
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=2
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和
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=3
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的夹角是( )
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![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131101222720113043696/SYS201311012227201130436007_ST/0.png)
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D.
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