使數(shù)列
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的前4項(xiàng)依次是20,11,2,-7的一個(gè)通項(xiàng)公式是( )
本題考查數(shù)列的通項(xiàng)公式.
從前四項(xiàng)看,這是一個(gè)以
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為首項(xiàng),以
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為公差的等差數(shù)列。由等差數(shù)列的通項(xiàng)公式有
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,故
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正確;
對(duì)于A,當(dāng)
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時(shí)
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,錯(cuò);
對(duì)于C,當(dāng)
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時(shí),
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,錯(cuò);
對(duì)于D,當(dāng)
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時(shí),
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,錯(cuò);
故正確答案為
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科目:高中數(shù)學(xué)
來(lái)源:不詳
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(本小題滿(mǎn)分12分)

數(shù)列
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的前
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項(xiàng)和為
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且

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(1)求數(shù)列

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
的各項(xiàng)均為正數(shù),其前

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
,

,又

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(本題滿(mǎn)分14分)
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的前
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均在
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函數(shù)
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的圖象上
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
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
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
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的前

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
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
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。
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
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,以及前
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項(xiàng)和
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;
(2)
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
的前n項(xiàng)的和

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數(shù)列
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
則
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來(lái)源:不詳
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已知數(shù)列
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共六項(xiàng),其中有三項(xiàng)都等于2,有兩項(xiàng)都等于
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
共有 個(gè)
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