设等差数列{an}前n项和为Sn,且a1>0,S13=S19,求Sn的最大值

设等差数列{an}前n项和为Sn,且a1>0,S13=S19,求Sn的最大值 设等差数列{an}的前n项和为Sn 若a1=Sn> 设Sn是等差数列{an}的前n项和,且S5S8,则a1 设等差数列{an}的前n项和为Sn,a1=3/2,且S1,S2,S4成等差数列,求Sn 设数列{an}的前n项和为Sn,其中an不等于0,a1为常数,且一a1,Sn,an十1成...设数列{an}的前n项和为Sn,其中an不等于0,a1为常数,且一a1,Sn,an十1成等差数列.求{an}的通项公式, 设等差数列{an}的前n项和为Sn,a1>0,S12>0,S13 设an是公差不为0的等差数列,a1=2且a1,a3,a6成等比数列,则an的前n项和Sn= 设an是公差不为0的等差数列,a1=2,且a1,a3,a6成等比数列,则an的前n项和Sn=? 设an是公差不为0的等差数列 a1=2 且a1 a3 a6成等比数列 则 an的前n项和Sn=? 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 等差数列｛an｝中,前n项和为sn,a1>0,且s12>0,s13 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a1^2+a8^2 设等差数列{an}满足3a8=5a13,且a1>0,Sn为其前n项和,则Sn中最大的是前几项和? 设数列an的前n项和为Sn,满足2Sn=an－2∧n+1 +1 ,且a1,a2+5,a3成等差设数列an的前n项和为Sn,满足2Sn=an－2∧n+1 +1 ,且a1,a2+5,a3成等差数列.求a1,an的通项 设数列An的前n项和为Sn,满足2Sn=An+1 -2^n+1+1,且A1.A2+5.A3成等差数列 求数列的设数列An的前n项和为Sn,满足2Sn=An+1 -2^n+1+1,且A1.A2+5.A3成等差数列 求数列的通项公式 记等差数列an的前n项和为Sn,设S3=12,且2a1,a2,a3+1成等比数列,求Sn