设数列
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的前n项和为
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,且
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对任意正整数n都成立,其中
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为常数,且
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,(1)求证:
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是等比数列;(2)设数列
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的公比
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,数列
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满足:
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,求数列
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的前
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项和
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。
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正项数列满足:
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,
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,点
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在圆
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上,
(1)求证:
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;
(2)若
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
,求证:数列

是等比数列;
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
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等差数列

中,
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A.24 | B.48  | C.72 | D. 108 |
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.已知数列
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为等比数列,且
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
的前
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项和为
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,则
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=__________.
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