等差数列{an}前n项和为Sn且6xS6-5xS5=5,则a4等于多少

等差数列{an}前n项和为Sn且6xS6-5xS5=5,则a4等于多少 等差数列｛an｝前n项和为Sn,且Sn=3n^2+n 求公差d 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,a10 等差数列{an}中,a1>0,前n项和为Sn,且S9>0,S10 等差数列an ,前n项和为Sn,a1>0,且s12>0,s13 Sn为等差数列{an}前n项和,且S10＞0,S11 设等差数列an前n项和为sn,且s10=s20.则s30=? 等差数列｛an｝中,前n项和为sn,a1>0,且s12>0,s13 已知等差数列An的前n项和为Sn,且S13>0,S14 等差数列{An}中,前n项和为Sn A1>0 且s12>0 s13 设等差数列{an}的前n项和为Sn,且满足S15>0,S16 等差数列an的前n项和为Sn,且a5+a21=a12,求S27 设等差数列｛an｝的前n项和为Sn,且S6 等差数列an的前n项和为sn 且s7=7 则a2+a6 已知等差数列an的前n项和为Sn,且a1^2+a8^2 等差数列{an}的前n项和为Sn,且S10-S5=3,S15=? 设Sn为等差数列{An}的前n项和,求证：{Sn/n}是等差数列