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        1. 已知方向上的投影為,則 

          A.3 B. C.2 D. 

          B

          解析試題分析:為兩向量的夾角。故選B。
          考點:數(shù)量積
          點評:本題需要理解數(shù)量積的幾何意義:向量 與的數(shù)量積等于向量)的模乘以向量)在向量)方向上的投影)。

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