已知等差数列an的前n项的和为Sn=48,S2n=60,S3n=?

(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 已知等差数列an中,前n项和sn=n^2-15n,则使sn为最小值的n 已知sn=32n-n^2求等差数列|an|的前n项和sn 等差数列an的前n项和为Sn,已知a5=11 a8=5求an和Sn 已知Sn为等差数列an的前n项和,a6=100,则S11= 已知Sn为等差数列｛an｝的前n项和,S11=55,则a6= 设等差数列{an}的前n项和为Sn,已知a3=11,S15*S16 已知等差数列{an}的前n项和为Sn,则S7-S3除以S10= 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=3n²-2n,证明数列{An}为等差数列 已知数列{an}的前N项和sn=n^2+n+1,an是否为等差数列? 已知数列{an}的前n项和Sn=-n^2+18n,求证:{an}为等差数列 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? 已知等差数列{An}的前n项和为Sn,已知A1=25 S9+S17 求Sn最大值 设Sn为等差数列an的前n项和.求证Sn/n为等差数列 等差数列an的前n项和为Sn,已知Sm=a,Sn-Sn-m=b,m、n属于自然数且n>m,求Sn? 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