設(shè)
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是等差數(shù)列,從

中任取3個不同的數(shù),使這3個數(shù)仍成等差數(shù)列,則這樣不同的等差數(shù)列的個數(shù)最多有( )
從
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,
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,

…
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中任選兩個作為等差數(shù)列的第一、三,等差中項唯一確定,只有一種選法,從
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,

,

…

中任選兩個作為等差數(shù)列的第一、三,等差中項唯一確定,只有一種選法。又數(shù)列有遞增和遞減之分,∴這樣的等差數(shù)列共有2


=180個。
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科目:高中數(shù)學
來源:不詳
題型:解答題
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,

.
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
⑶設(shè)

,且

,證明:

.
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
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
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
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
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等差數(shù)列{
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am=

,
ak=

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
中,

(I)設(shè)

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
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
的前

項和

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
的前

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
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
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
}滿足

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
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
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
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
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
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
,點

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
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
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
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
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