数列{An}前n项和为Sn,已知A1=1,且满足3Sn^=An(3Sn-1)(>=2)
来源:百度知道 编辑:UC知道 时间:2024/05/24 22:41:47
数列{An}前n项和为Sn,已知A1=1,且满足3Sn^=An(3Sn-1)(>=2)
(1)求证:{1/Sn}是等差数列:
(2)设Bn=Sn/(3n+1),求数列{Bn}前n项和Tn
第一问不懂啊
(1)求证:{1/Sn}是等差数列:
(2)设Bn=Sn/(3n+1),求数列{Bn}前n项和Tn
第一问不懂啊
(1)证明:3Sn^2=An(3Sn-1),即
3Sn^=[Sn-S(n-1)](3Sn-1)=3Sn^2-Sn-3SnS(n-1)+S(n-1),即
1/Sn-1/S(n-1)=3
所以{1/Sn}是等差数列
(2)1/Sn=1/s1+d(n-1)=1/A1+3(n-1)=3n-2
Sn=1/(3n-2)
Bn=Sn/(3n+1)=1/[(3n-2)(3n+1)]
Tn=1/(1*4)+1/(4*7)+1/(7*10)+.....+1/[(3n-2)(3n+1)]
=[(1-1/4)+(1/4-1/7)+(1/7-1/10)+.....+1/(3n-2)-1/(3n+1)]/3
=[1-1/(3n+1)]/3
=n/(3n+1)
已知数列{An}的前n项和为Sn,且Sn=2-2An.
已知数列an的前n项和为Sn,且Sn=2-2an
急救!数列{an}中,a1=2,前n项和为Sn=n^2*an,求Sn
数列{an}的前n项和为Sn,且对任意正整数n, an+ Sn=4096.
设数列{an}的前n项和为Sn,且对任意正整数n,an+Sn=4096
已知数列(an)的前n项和为Sn,首项为a1,且1,an,Sn 成等差数列
设数列{an}的前n项和为Sn=2n^2...
已知数列{an}的前n项和为Sn,且a1=1,an+1=Sn(n+2)/n ,(n 属于 N*)求(1)数列{Sn/n}是等比数列(2)Sn+1=4an
已知数列{an}中,an>0,前n项和为Sn,且满足Sn=1/8(an+2)^2.求证数列{an}是等差数列。
数列{an}的前n项和为Sn,已知log2(Sn+2)=n+1