等差数列｛An｝的前n项和为Sn(n=1,2,3…)若当首项a1和公差d变化师时,a5＋a8＋a11是一个定值则下列选项中为定值的是( )A.S17 B.S18 C.S15 D.S14

(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 设Sn为等差数列an的前n项和.求证Sn/n为等差数列 数列an ,a1=1,前n项和为Sn ,正整数n对应的n an Sn 成等差数列.1.证明{Sn+n+2}成等比数列,2.求{n+2/n(n+1)(1+an)}前n项和 设Sn为等差数列{An}的前n项和,求证：{Sn/n}是等差数列 已知数列{an}的前N项和sn=n^2+n+1,an是否为等差数列? 等差数列{an}的前n项和为sn,a10 已知等差数列{an}的前n项和为Sn,如果Sn=(an+1/2)^2(n∈N+0,bn=(-1)^n*Sn已知等差数列{an}的前n项和Sn,如果Sn=(an+1/2)^2(n∈N+0,bn=(-1)^n*Sn,试求{bn}的前n项和Tn 等差数列{an}前n项和为sn,求证S2n-1=(2n-1)an 已知等差数列an中,前n项和sn=n^2-15n,则使sn为最小值的n 等差数列{an}的通项公式an=1-2n,其前n项和sn,则数列{sn/n}的前11项和为? 已知等差数列{an}的前n项和为Sn,满足关系lg(Sn+1)=n (n∈N*).试证明数列{an}为等比数列 等差数列an的前n项和为Sn=n^2+4n-1,则通项公式为? 设等差数列{an}的前n项和为Sn 若a1=Sn> 等差数列前n项和为Sn=1/2(An+1/An),求通项An 关于等差数列前n项和的问题思路 例题 等差数列中{an}的前n项和为Tn,{bn}的前n项和为Sn Tn/Sn=2n/m+1 求a8/b8 ,an/bn 等差数列{an}前n项和为Sn=3n-2n^2,求an 已知sn=32n-n^2求等差数列|an|的前n项和sn 等差数列{an}前n项和Sn=-n²+n,求等差数列的首项