设Sn是等差数列{an}前n项和,若以点O(0,0),A(l,Sl),B(m,Sm),C(p,Sp)为顶点的四边形(其中l

设Sn为等差数列{An}的前n项和,求证：{Sn/n}是等差数列 设｛an｝是等差数列前n项和为Sn,若S4>=10,S5 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. 设等差数列{an}的前n项和为Sn 若a1=Sn> 设Sn为等差数列an的前n项和.求证Sn/n为等差数列 设等差数列{an}公差d是2,前n项和为Sn,则lim(an^2-n^2)/Sn 设等差数列{an}公差d是2,前n项和为Sn,则lim(an^2-n^2)/Sn 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Sn是等差数列{an}的前n项和,且S5S8,则a1 设数列｛an｝的前n项和为sn,若对于所有的正整数n,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,若对于所有的正整数n,都有sn=n（a1+an）/2,证明｛an｝是等差数列 设Sn是等差数列{an}前n项和,若以点O(0,0),A(l,Sl),B(m,Sm),C(p,Sp)为顶点的四边形(其中l 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Sn是等差数列{an}的前N项和,若S7=35,则a4为几? 设Sn是等差数列｛an｝的前n项和,若S7=35,则a4= 有人吗