设数列{an}满足a1+3a2+3^2a3+3^3a4+······+3^n-1×an=3分之n,n属于N* 【1】求数列,{an}的通项公式【2】设b=a的n次幂分之n,求数列{bn}的前n项和sn

来源:学生作业帮助网 编辑:六六作业网 时间:2024/11/01 07:24:12
设数列{an}满足a1+3a2+3^2a3+3^3a4+······+3^n-1×an=3分之n,n属于N*【1】求数列,{an}的通项公式【2】设b=a的n次幂分之n,求数列{bn}的前n项和sn设

设数列{an}满足a1+3a2+3^2a3+3^3a4+······+3^n-1×an=3分之n,n属于N* 【1】求数列,{an}的通项公式【2】设b=a的n次幂分之n,求数列{bn}的前n项和sn
设数列{an}满足a1+3a2+3^2a3+3^3a4+······+3^n-1×an=3分之n,n属于N* 【1】求数列,{an}的通项公式
【2】设b=a的n次幂分之n,求数列{bn}的前n项和sn

设数列{an}满足a1+3a2+3^2a3+3^3a4+······+3^n-1×an=3分之n,n属于N* 【1】求数列,{an}的通项公式【2】设b=a的n次幂分之n,求数列{bn}的前n项和sn
1、a1+3a2+3^2a3+3^3a4+······+3^n-1×an=3分之n
a1+3a2+3^2a3+3^3a4+······+3^n-2×a(n-1)=3分之n-1
两式相减3^n-1×an=1/3
即an=1/3^n
2、bn=n/a^n
sn=1/a+2/a^2+3/a^3+……+n/a^n
(1/a)sn=1/a^2+2/a^3+……+n/a^(n+1)
(1- 1/a) sn=1/a+1/a^2+1/a^3+……+1/a^n-n/a^(n+1)
(1- 1/a) sn=(1+1/a^n)/(a-1)-n/a^(n+1)
sn=.
这是乘公比错位相减法,经常用的
best wish

设数列{an}满足:a1+a2/2+a3/3+a4/4……+an/n=An+B,其中A、B为常数.数列{an}是否为等差数列? 设数列AN满足A1等于1,3(A1+a2+~+AN)=(n+2)an,求通向公式 设数列{an}满足;a1+a2/2+a3/3+...+an/n=n^2-2n-2,求数列{an}的通项公式(a1,a2,a3...an中a后面都是下标) 设数列an满足a1=1,a2=4,a3=9,an=a(n-1)+a(n-2)-a(n-3).则a2011= 已知数列{an}满足对任意的正整数n,都有an>0,且a1^3+a2^3+..an^3=(a1+a2..an)^2,设数列{1/an*an+2}设数列{1/an*an+2}的前n项和为Sn,不等式Sn>1/3loga(1-a)对于任意正整数n恒成立,求实数a的取值范围 设数列{an}满足a1+2a2+3a3+.+nan=n(n+1)(n+2)求通项an 设数列【an】满足a1=1,3(a1+a2+a3+······+an)=(n+2)an,求通项an 设数列an满足a1+2a2+3a3+.+nan=2^n 1求数列a的通项 2设bn=n^2an 求数列的前n项和Sn求大神帮助 问道数列题.设数列an满足a1+2a2+3a3+...+nan=2^n(n属于正自然数),则数列an的通项是? 设数列an满足a1+3a2+3^2a3+……+3^(n-1)an=n/3,a是正整数,设bn=n/an,求数列bn的前n项和 设数列{an}满足a1+a2/2+a3/3+.+an/n=n^2-2n-2,求数列{an}的通项公式 (1)数列{an}中,a1=1,a2=-3,a(n+1)=an+a(n+2),则a2005=____(2)已知数列{an}满足a1=1,a1×a2×a3…an=n^2,求an. 已知数列{an}满足a1=1,a2=3,a(n+2)=a(n+1)-an,求S2012 设数列{an}和{bn}满足a1=b1=6,a2=b2=4,a3=b3=3 ,且数列{an+1-an}是等差数列设数列{an}和{bn}满足a1=b1=6,a2=b2=4,a3=b3=3 ,且数列{a(n+1)-an}是等差数列,{bn-2}是等比数列(2)设{nbn}的前n项和为Sn,求Sn的表达式(3)数列{C 设数列{an}满足a1+2a2+3a3+······nan=n^2求数列{an}的通项公式 设数列{an}满足a1+3 a2+3^2 a3+……+3^n-1 an=n/3,a属于N* 求数列{an}的通项谢谢大家呐``` 设数列an的前n项和为Sn,满足an+Sn=An^2+Bn+1(A不等于0),a1=3/2,a2=9/4,求证an-n为等比数列并求an 数列an满足n ∈ N*,an > 0 且a1^3 + a2^3 + a3^3 + ...+ an^3 = (a1 + a2 + a3 + ...+ an)^2设数列1 / [ an * a(n+2) ] 的前n项和为Sn,不等式Sn > log (a) (1-a) / 3 对任意正整数n 恒成立,求实数a 的取值范围.0 < a < 1/2,我另