((本小题满分14分)在数列,中,a1=2,b1=4,且成等差数列,成等比数列()(Ⅰ)求a2,a3,a4及b2,b3,b4,由此猜测,的通项公式,并证明你的结论;(Ⅱ)证明:.-高三数学

题目简介

((本小题满分14分)在数列,中,a1=2,b1=4,且成等差数列,成等比数列()(Ⅰ)求a2,a3,a4及b2,b3,b4,由此猜测,的通项公式,并证明你的结论;(Ⅱ)证明:.-高三数学

题目详情

((本小题满分14分)
在数列中,a1=2,b1=4,且成等差数列,成等比数列(
(Ⅰ)求a2a3a4b2b3b4,由此猜测的通项公式,并证明你的结论;
(Ⅱ)证明:
题型:解答题难度:偏易来源:不详

答案

由条件得
由此可得
.································ 2分
猜测.································································ 4分
用数学归纳法证明:
①当n=1时,由上可得结论成立.
②假设当n=k时,结论成立,即

那么当n=k+1时,

所以当n=k+1时,结论也成立.
由①②,可知对一切正整数都成立.······························· 7分
(Ⅱ)
n≥2时,由(Ⅰ)知.·································· 9分



综上,原不等式成立. ············································································ 14分

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