已知
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,
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是兩個相互垂直的單位向量,而
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,
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,
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,則對于任意實數(shù)
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,
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的最小值是( )
解:因為
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,
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是兩個相互垂直的單位向量,而
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,
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,
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,則對于任意實數(shù)
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,
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因為
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,代入表達式中可知,
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的最小值是12
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在直角梯形
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∥
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,
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,
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
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已知
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是同一平面內(nèi)的三個向量,其中

.
(1)求與
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平行的單位向量

的坐標;
(2)若
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,且
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與
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.
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