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已知方向上的投影为,则 

A.3 B. C.2 D. 

B

解析试题分析:为两向量的夹角。故选B。
考点:数量积
点评:本题需要理解数量积的几何意义:向量 与的数量积等于向量)的模乘以向量)在向量)方向上的投影)。

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