已知數(shù)列
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是首項
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,公比為
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的等比數(shù)列,
(1)證明:
(2)計算:
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(1)見解析(2)
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試題分析:(1)運用排列組合公式進行求證;(2)先令通項
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分
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和
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討論,注意借助(1)中的結(jié)論.
(1)
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故等式成立.
(2)設(shè)
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(i)當(dāng)
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時,
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(ii)當(dāng)
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時,
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故
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