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精英家教網 > 高中數學 > 題目詳情

(Ⅰ)若,求實數的值;
(Ⅱ)求方向上的正射影的數量.
(Ⅰ)(Ⅱ)

試題分析:(Ⅰ)
 所以  5分
(Ⅱ)……10分
點評:若,若的夾角為,則方向上的投影為
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