已知數(shù)列
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是等差數(shù)列,且
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(1)求數(shù)列

的通項公式
(2)令
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,求數(shù)列
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前n項和
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.
(1)
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;(2)
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.
試題分析:(1)直接利用等差數(shù)列的通項公式求出公差
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,再寫出通項公式;(2)數(shù)列
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可看作是由一個等差數(shù)列
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和等比數(shù)列
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對應(yīng)項相加得到的數(shù)列,其前
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和可用分組求和法求和.
試題解析:(1)
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,又
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,
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.
∴
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. 5分
(2)
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,
∴
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. 12分
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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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
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,

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
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
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,
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是
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和

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
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
的前

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.
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
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
,則

等于( )
A.—1 | B. | C. | D.1 |
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在一個數(shù)列中,如果對任意
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,都有
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為常數(shù)

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
叫做這個數(shù)列的公積.已知數(shù)列
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是等積數(shù)列,且

,公積為
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,則
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( )
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在等差數(shù)列
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中,
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,其前
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項和為
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,若
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,則
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的值等于
.
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