(本小題滿分10分)
平面向量
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已知
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∥
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,
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,求
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、
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及
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夾角.
解: 由
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且
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//

得
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,所以
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,即
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;
由
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且
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得
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,所以
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,即
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;
又
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,故
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與
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夾角為
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(或由
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得到)
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
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
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
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
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
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
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
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
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