設等差數(shù)列
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的公差不等于0,且其前n項和為
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。若
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且
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成等比數(shù)列,則
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試題分析:由
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得
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,化簡得:
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。又由
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有
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,化簡得:
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。因
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,故
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。由
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得:
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。故
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。選A。
點評:從已知出發(fā),布列“基本量”的方程組,是解答數(shù)列問題的基本思路。本題對學生計算能力要求較高。
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(本題滿分12分)已知數(shù)列
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的各項均為正實數(shù),且其前
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項和
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滿足
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。(1)證明:數(shù)列
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是等差數(shù)列;
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
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
的前
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項和

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的前
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項和為
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.已知
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,
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,
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(2)記
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為數(shù)列

的前
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項和,求
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;
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
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
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三點共線,
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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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