已知数列{an}满足:an+1=an+2,a1=3,前n项和为Sn,求数列{an}的通项公式,求1/S1+1/S2+…+1/Sn
来源:学生作业帮助网 编辑:作业帮 时间:2024/11/06 03:17:51
已知数列{an}满足:an+1=an+2,a1=3,前n项和为Sn,求数列{an}的通项公式,求1/S1+1/S2+…+1/Sn
已知数列{an}满足:an+1=an+2,a1=3,前n项和为Sn,求数列{an}的通项公式,求1/S1+1/S2+…+1/Sn
已知数列{an}满足:an+1=an+2,a1=3,前n项和为Sn,求数列{an}的通项公式,求1/S1+1/S2+…+1/Sn
∵an+1=an+2
∴an+1-an=2
∴an为公差为2首项为3的等差数列
∴an=2n+1
Sn=n(2n+4)/2=n(n+2)
∴1/Sn=1/n(n+2)=(1/2)*[1/n-1/(n+2)]
则1/S1+1/S2+…+1/Sn=1/2[1-1/3+1/2-1/4+1/3-1/5-1/n+2]=n+1/2n+4
a
an=2n+1
Sn=n^2+2n=n(n+1)
1/sn=1/n-1/(n+1)
1/S1+1/S2+…+1/Sn
=1/1-1/2+1/2-1/3+......1/n-1/(n+1)
=1-1/(n+1)
=n/(n+1)
怎么能让祖国的花朵算这种题目呢。蛋疼。。
第二问应该是3\4-(2n+3)\2(n+1)(n+2)吧。
月风千杀舞 的 裂项相消 过程有点儿问题。
已知数列{an}满足an+1=2an+3.5^n,a1=6.求an
已知数列{an}满足a1=1 an+1=an/(3an+1) 则球an
已知数列an满足 a1=1/2,an+1=3an/an+3求证1/an为等差数列已知数列an满足 a1=1/2,an+1=3an/an+3求证1/an为等差数列
已知数列an满足a1=1,1/an+1=根号1/an^2+2,an>0,求an
已知数列{an}满足a1=1,a2=3,an+2=3an+1-2an求an
已知数列{an}满足a1=1,an+1 -an+2an+1•an=0求通项
已知数列{an}满足a1=2,an+1=2an/an+2,则an等于多少
已知数列{an}满足a1=2,an+1-an=an+1*an,那么a31等于
已知数列{An}满足A1=1,An+1=2An+2^n.求证数列An/2是等差数列
已知数列{an}满足a1=1/2,an+1=3an+1,求数列{an}通项公式
已知数列满足a1=1 ,an+1+2an=2 求an
已知数列an满足条件a1=-2 an+1=2an+1则a5
已知数列an满足an=1+2+...+n,且1/a1+1/a2+...+1/an
已知数列{an}满足a1=1,an+1·an=2^n 则s2012
已知数列{an}满足An+1=2^nAn,且A1=1,则通项an
已知数列{an}满足a1=1/2,sn=n^2an,求通项an
已知数列{an}满足a1=1,an+1=2an+1 1)求证:数列{an+1}为等比数列; 2) 求{an}的通项an
已知数列{an},满足a1=1/2,Sn=n²×an,求an