已知等比數(shù)列
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的前n項和為
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,若
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,則
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___________.
試題分析:利用等比數(shù)列前
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項公式 展開時,需討論公比
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是否為1,∵
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,∴
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,
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,
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,聯(lián)立得
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=
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=33
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項和.
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
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