(本題12分)
已知向量
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,
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,且
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(1)求
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及
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;
(2)求函數(shù)
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的最小值
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.
(1)
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,
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,得
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(
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,
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).
(2)
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令
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,
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,則
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下面分類討論
(1) 當(dāng)
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,即
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時,當(dāng)
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時,
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,此時
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;
(2) 當(dāng)
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,即
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時,當(dāng)
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時,
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,此時
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;
(3) 當(dāng)
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,即
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時,當(dāng)
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時,
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,此時
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.
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設(shè)
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,
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為坐標(biāo)原點,動點
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滿足
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,
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,則
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的最大值是 ( )
A.-1 | B.1 | C.-2 | D. |
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.下列命題中:
①
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∥
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存在唯一的實數(shù)
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,使得
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;
②
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為單位向量,且
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∥
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,則
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=±|
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|·
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;③
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;
④
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與
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共線,
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與
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共線,則
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與
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共線;⑤若
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