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科目:高中数学
来源:不详
题型:解答题
已知
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,数列
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是首项为
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,公比也为

的等比数列,令

(Ⅰ)求数列

的前
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项和
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;
(Ⅱ)当数列

中的每一项总小于它后面的项时,求

的取值范围.
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科目:高中数学
来源:不详
题型:解答题
已知数列

满足:①
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;②对于任意正整数
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都有

成立.
(Ⅰ)求

的值;
(Ⅱ)求数列

的通项公式;
(Ⅲ)若

,求数列

的前
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项和.
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科目:高中数学
来源:不详
题型:单选题
已知正项等比数列
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满足
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.若存在两项

使得
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,

的最小值为( )
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科目:高中数学
来源:不详
题型:填空题
等比数列

中,若公比
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,且前3项之和等于21,则该数列的通项公式
.
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科目:高中数学
来源:不详
题型:单选题
设S
n为等比数列{a
n}的前n项和,若
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,则
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( )
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