题目内容
(本小题满分12分) 已知函数,数列,满足条件:.
(1)求证:数列为等比数列;
(2)令,Tn是数列的前n项和,求使成立的最小的n值.
(1)求证:数列为等比数列;
(2)令,Tn是数列的前n项和,求使成立的最小的n值.
解:(1) 证明:由题意得,
∴········································································ 3分
又∵
∴················································································ 4分
故数列{bn + 1}是以1为首项,2为公比的等比数列············································· 5分
(2) 由 (1) 可知,,∴·········································· 7分
故················································ 9分
∴
············································ 10分
由,得
∴满足条件的n的最小值为10···································································· 12分
∴········································································ 3分
又∵
∴················································································ 4分
故数列{bn + 1}是以1为首项,2为公比的等比数列············································· 5分
(2) 由 (1) 可知,,∴·········································· 7分
故················································ 9分
∴
············································ 10分
由,得
∴满足条件的n的最小值为10···································································· 12分
略
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