等差数列{an}的前n项和Sn=48,前3n项的和S3n=36,则前2n项的和S2n等于什么

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 等差数列{an}的前n项和为sn,a10 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 已知等差数列{an}前n项和Sn=-2n2-N,求通项an的表达式 已知等差数列{an}的前n项和Sn=n²求an 设等差数列{an}的前n项和为Sn 若a1=Sn> 等差数列{an}的前n项和Sn=m,前m项和Sn=n(m>n),求前m+n项和Sm+n (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 等差数列{an}的前n项和sn=an^2+bn+c,则c= 已知等差数列{an}的前n项和是sn=32n一n*n,求{|an|}的前n项和sn 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的前n项和Sn=(n+1)²+λ,则λ= 等差数列an的前n项和为Sn,已知a5=11 a8=5求an和Sn 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｝前n项和Sn=n平方-20n,求｛|an|｝前n项和Tn.已知等差数列｛an｝前n项和Sn=n²-20n,求｛|an|｝前n项和Tn.