设等差数列{an}的前n项和为Sn,且满足S15>0,S16

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,且满足S15>0,S16 设等差数列｛an｝的前n项和为Sn,且S6 设等差数列{an}前n项和为Sn,且a1>0,S13=S19,求Sn的最大值 设等差数列An的前n项和为Sn,且S4=4S2,A2n=2An+1 设数列{an}为正项数列,前n项的和为Sn,且an,Sn,an^2成等差数列,求an通项公式 设等差数列{an}的前n项和为Sn,且S5=-5,S10=15,求数列{Sn/n}的前n项和Tn 设等差数列{an}的前n项和为Sn 若a1=Sn> 设等差数列an前n项和为sn,且s10=s20.则s30=? 设等差数列{an}的前n项和为Sn,且a4-a2=8,S10=190,(1)求等差数列{an}的通项公式an 设等差数列{an}的前n项和为Sn ,且S15>0,a8+a90,a8+a9 设等差数列｛An｝的前n项和为Sn,且A5＝5A3,则S9/S5＝? 设等差数列{an}的前n项和为Sn,已知a3=12,且S12>0,S13 设等差数列{an}的前N项和为Sn,且a3+a5+a7=15,则S9=? 设等差数列{an}的前n项和为Sn,已知a4=12,且S8>0,S9 设等差数列{an}的前n项和为Sn,且a5=3a7,则S9/S13=? 设等差数列{an}的前n项和为Sn,且S4=20,S8=72,则S12=?