设Sn是等差数列{an}的前n项和,已知1/3S3,1/4S4的等比中项为1/5S5,1/5S5与1/4S4的等差中项为1,求an

设Sn为等差数列{An}的前n项和,求证：{Sn/n}是等差数列 设Sn为等差数列{an}的前n项和,已知a6+a70,那么Sn中最小的是 设Sn为等差数列{an}的前N项和,已知 a6 +a70,那么Sn 中最小的是 设Sn是等差数列{an}的前n项和,已知S6=36,Sn=324,Sn-6=144（n>6),则n等于? 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}的前n项和为Sn,已知a3=11,S15*S16 设等差数列{an}的前n项和为Sn,已知S12>0,S13 设等差数列{an}的前n项和sn,已知a3=12,s12>0.s13 设Sn是等差数列an的前n项和,已知a2=3,S11=121,则S7等于 已知等差数列{an}中Sn是它的前n项和,设a6=2,S10=10 设Sn是等差数列｛an｝的前n项和,已知a1=3,a2=11,则S7等于? 设Sn是等差数列 an 的前n 项和,已知a2=3,a6=11,求S7. 设Sn是等差数列{an}的前n项和,已知a2=3,a6=11,则S7=? 设Sn是等差数列｛an｝的前n项和,已知a2=3,a6=11,则S7等于? 设Sn是等差数列(an)的前n项和,已知a2等于3,a6等于11,则S7等于 设Sn是等差数列｛an｝的前n项和,已知a2=3,S11=121,则S7= (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 设Sn是等差数列{an}的前n项和,已知S8=108,Sn=630,S(n-8)=234,求n.