已知数列〔an〕是等差数列,sn是前n项之和,求证s6,s12_s6,s18-s12也成等差数列

(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 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｝的前n项和sn=n方+3n,求证数列{an}是等差数列 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 已知数列〔an〕是等差数列,sn是前n项之和,求证s6,s12_s6,s18-s12也成等差数列 已知数列an是等差数列,且a1不等于0,Sn为这个数列的前n项和,求limnan/Sn.limSn+Sn-1/Sn+Sn-1 已知数列{an}中,a2=2,前n项和为Sn,且Sn=n(an+1)/2证明数列{an+1-an}是等差数列 已知数列{an}的前n项和Sn=100n-n^2,证明{an}是等差数列 已知数列{an}中,an>0,前n项和为Sn,且满足Sn=1/8(an+2)^2.求证数列{an}是等差数列. 等差数列的证明问题已知数列{an}的前n项和Sn=n(a1+an)/2，求证数列{an}是等差数列。 已知数列{An}的前N项和Sn=4n2+3n,求证{An}是等差数列 已知数列an其前n项和为Sn,且Sn=3n^2+5n,求证数列an是等差数列 已知数列{An}的前N项和Sn,求Sn^(1/2)是等差数列的充要条件 已知数列{an}的前n项是sn=2n²-n.书这个数列的通项公式an?证明此数列是等差数列? 已知公差不为0的等差数列{An}的首项A1=1,前n项和为Sn,若数列{Sn/An}是等差数列,求An? 已知数列{an}的前n项和为Sn,且满足an+2Sn*Sn-1=0,a1=1/2.求证：{1/Sn}是等差数列 高二超难数列题!已知数列an的前n项和为Sn=n平方-3n 求证数列an是等差数列 已知Sn为等差数列An的前n项和,Bn=Sn/n(n属于正整数）,求证：数列Bn是等差数列