①设an是等差数列,求证：{Sn/n}是等差数列

设Sn是等差数列｛an｝的前n项和,求证：若正整数m,n,p成等差数列,则Sm/m,Sn/n,Sp/p也成等差数列. 一道关于等差数列的题设Sn为等差数列｛An｝的前n项和 求证：数列｛n分之Sn}是等差数列 设数列an的前n项和为sn,对于所有的自然数n都有sn=n(a1+an)/2,求证an是等差数列 已知在数列an中,Sn=2n^2+3n,求证an是等差数列 设Sn是等比数列｛an｝的前n项和,s3,S9,S6,成等差数列求证:a2,a8,a5　成等差数列 设数列{an}的前n项和为Sn ,求证数列{an}成等差数列的充要条件是：对一切m,n∈N*,都有 已知数列{an}的前n项和sn满足sn=an^2+bn,求证{an}是等差数列 设Sn是等比数列的前n项和,S3,S9,S6成等差数列 求证a2,a8,a5成等差数列 设Sn是等比数列{an}的前n项和，S3，S9，S6成等差数列． 设Sn是等差数列{an}的前n项和，若a 设数列{an}的前n项和为Sn,a1=1,an=sn/n+2(n-1),求证数列{an}是等差数列,并求其通项公式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