(本小题满分12分)设数列的前项和为。已知,,。(Ⅰ)设,求数列的通项公式;(Ⅱ)若,,求的取值范围。-高三数学

题目简介

(本小题满分12分)设数列的前项和为。已知,,。(Ⅰ)设,求数列的通项公式;(Ⅱ)若,,求的取值范围。-高三数学

题目详情

(本小题满分12分)
设数列的前项和为。已知
(Ⅰ)设,求数列的通项公式;
(Ⅱ)若,求的取值范围。
题型:解答题难度:中档来源:不详

答案

(Ⅰ)
(Ⅱ)
(Ⅰ)依题意,,即
由此得。·································································· 4分
因此,所求通项公式为
。①·························································· 6分
(Ⅱ)由①知
于是,当时,





时,



综上,所求的的取值范围是。····················································· 12分

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