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        1. 已知,且的夾角為120°.
          求:(1)  ;         (2) ;       (3) .
          (1)-1
          (2)-5
          (3)

          試題分析:(1)     ……4分
          (2)   ……8分
          (3)
          點(diǎn)評(píng):主要是考查了向量的數(shù)量積的坐標(biāo)運(yùn)算,屬于基礎(chǔ)題。
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