(本小題滿分12分)
已知數(shù)列
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滿足
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,
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,
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(Ⅰ)設(shè)
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的通項公式;
(Ⅱ)求
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為何值時,
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最小(不需要求
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的最小值)
(I)
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;(Ⅱ)當n=8或n=9時,a
n的值相等并最小。
(I)
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即數(shù)列{b
n}的通項公式為
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(Ⅱ)若
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最小,則
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注意n是正整數(shù),解得8≤n≤9
∴當n=8或n=9時,a
n的值相等并最小
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
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