设等差数列{an}的前n项和为Sn 若a1=Sn>

来源：学生作业帮助网编辑：六六作业网时间：2024/12/22 09:34:25

设等差数列{an}的前n项和为Sn若a1=Sn>设等差数列{an}的前n项和为Sn若a1=Sn>设等差数列{an}的前n项和为Sn若a1=Sn>1.S2013=(a1+a2013)*2013/2=0a

设等差数列{an}的前n项和为Sn 若a1=Sn>
设等差数列{an}的前n项和为Sn 若a1=Sn
>

设等差数列{an}的前n项和为Sn 若a1=Sn>
1.S2013=(a1+a2013)*2013/2=0
a1+a2013=0 a10
所以 d>0
a1+a2013=2a1007=0
a1007=0
前1006项都为负数,所以S1006最小,n=1006
2.a2013=a1+2012d=0
a1=-2012d
Sn=na1+n(n-1)d/2=-2012nd+n(n-1)d/2
an=a1+(n-1)d=-2013d+nd
an-Sn
=-2013d+nd+2012nd-n(n-1)d/2
=2013d(n-1)-n(n-1)d/2
=d(n-1)(2013-n/2)
=d/2(n-1)(4026-n)>=0 d>0
(n-1)(n-4026)

设Sn为等差数列an的前n项和.求证Sn/n为等差数列设Sn为等差数列{An}的前n项和,求证：{Sn/n}是等差数列设等差数列{an}的前n项和为Sn 若a1=Sn> 设等差数列an的前n项和为Sn,若S4>=10,S5 设等差数列{AN}的前N项和为SN,若S9>0,S10 设等差数列 {an}的前n 项和为Sn,若S9>0 ,S10 在等差数列{an},设Sn为它的前n项和,若S15>0,S16 设等差数列{an}的前n项和为Sn,若-a2013 设数列an的前n项和为Sn,满足an+sn=An^2+Bn+1(A不等于0)an为等差数列,求(B-1)/A 设等差数列an的前n项和为Sn,若Sn＝3,S3n＝15,则S5n等于? 设等比数列｛an｝的公比为q,前n项和为Sn,若Sn+1,Sn,Sn+2成等差数列,则q的值为设等比数列{An}的公比为q,前n项和为Sn,若Sn+1,Sn,Sn+2成等差数列,则q的值为（）设等比数列an的公比为q 前n项和为Sn 若Sn+1 Sn Sn+2成等差数列则q的值设等差数列{an}的前n项和为Sn,若a6=S3=12,则an=多少? 设等差数列{an}的前n项和为Sn,若a6=S3=12,则an=? 设数列{an}的前n项和为Sn,若对任意正整数,都有Sn=n(a1+an)/2,证明{an}是等差数列. 设数列{an}的前n项和为Sn,若{an}和{根号sn+n}都是公差为d的等差数列,则a1= 设等差数列{an}的首项a1为a,前n项和为Sn,若S1S2S3成等比数列求数列{an}的通项公式…