等差数列{an}前n项和为sn,求证S2n-1=(2n-1)an

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 数列An为等差数列,其前n项和为Sn 且a3=7,a5=11.求证1/s1+1/s2+.+1/Sn 等差数列an,前n项和为sn,a3=6,s3=12求证：1/s1+1/s2+...+1/sn 等差数列{an}前n项和为sn,求证S2n-1=(2n-1)an 已知an是等差数列,前n项和为Sn,求证:S3n=3(S2n-Sn) 已知等差数列（an}得公差d不等于零,前n项的和为Sn 求证：点P1（1,S1/1),(2,S2/2),(3,S3/3).(n,Sn/已知等差数列（an}得公差d不等于零,前n项的和为Sn 求证：点P1（1,S1/1),(2,S2/2),(3,S3/3).(n,Sn/n)在同一条直线 等差数列{an}=2n+1,前n项和为Sn,求1/S1+1/S2+.+1/Sn (1)已知数列an的前n项和为sn满足sn=an²+bn,求证an是等差数列(2)已知等差数列an的前n项和为sn,求证数列sn/n也成等差数列 等差数列前n项和为Sn,求证:S2n-1=(2n-1)an 等比数列an前n项和sn满足s1,s3,s2成等差数列,求sn 设等差数列An的前n项和为Sn,且S4=4S2,A2n=2An+1 等比数列{an},前n项和为Sn,若S1,2S2,3S3成等差数列,求{an}的公比 等比数列{an}的前n项和为Sn.S1.2S2.3S3诚等差数列,则{An}的公比 等差数列 an 的前n项和为sn,令Tn=1/s1+1/s2+...等差数列an=2n的前n项和为Sn,令Tn=1/S1+1/S2+...+1/Sn,求证：Tn＜1 等差数列{an}前n项和为Sn,求证S 2n-1项=（2n-1）an 已知数列{an}的前n项和为Sn=n^2-3n,求证：数列{an}是等差数列 已知数列an前n项的和sn＝n²－9n求证an为等差数列