等差数列｛an｝的首项a1>0,前n项和为sn,且sm=sn(m,k为常数且m≠k),则①s(m+k)=?②当n为何值：sn值最大等差数列｛an｝的首项a1>0,前n项和为sn,且sm=sk(m,k为常数且m≠k),则①s(m+k)=?②当n为何值：sn值最大

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? 设等差数列{an}的前n项和为Sn,a1>0,S12>0,S13 设等差数列{an}的首项a1及公差d都为整数,前n项和为sn.若a1>=6,a11>0,s14 等差数列an中,a1=-60,a17=-12,求其前n项绝对值的和 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 已知等差数列an的前n项和为Sn,且a1^2+a8^2 等差数列{an}中,a1>0,前n项和为Sn,且S9>0,S10 等差数列{an}中,前n项和为Sn,a1>0,S12>0,S13 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 等差数列{an}前n项和Sn 已知lim [Sn/(n²+1）]=-a1/8（a1>0) 则Sn达到最大值时的n=__ 等差数列{an}前n项和Sn 已知lim [Sn/(n²+1）]=-a1/8（a1>0) 则Sn达到最大值时的n=__ 等差数列｛an}中,前N项和为sn,s5=s13,a1>0,则前n项和最大时的n=? 等差数列｛an｝3a4=7a7,且a1>0sn是等差数列｛an｝的前n项和,若sn取最大值, 设{an}是公差不为0的等差数列,a1=2,a1、a3、a6成等比数列,求{an}的前n项和Sn的值 等差数列{an}中,已知a1>0,Sn为数列的前n项和,若S9>0,S10