已知是夾角為60°的兩個(gè)單位向量,則的夾角的余弦值是(    )

A.B.C.D.

D

解析試題分析:   
,同理 
考點(diǎn):兩向量夾角
點(diǎn)評(píng):設(shè)的夾角為,則,

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