等差数列.公差为d.前n项合为Sn=-n²,则通项公式和公差分别为?

等差数列.公差为d.前n项合为Sn=-n²,则通项公式和公差分别为? 等差数列｛an｝前n项和为Sn,且Sn=3n^2+n 求公差d 已知公差为d的等差数列的前n项之和为Sn,则Sn+1/n+1-Sn/n 已知等差数列前n项和为Sn=2n^2+an,a为常数,则公差d= 记数列{an}的前n项和为Sn,若{Sn/an}是公差为d的等差数列,则{an}为等差数列的充要条件是d=? 设等差数列{an}公差d是2,前n项和为Sn,则lim(an^2-n^2)/Sn 设等差数列{an}公差d是2,前n项和为Sn,则lim(an^2-n^2)/Sn 等差数列{an}的前n项和为Sn,公差d 等差数列{an}中,公差为d,已知a4=84,前n项和为Sn,且S10>0,S11 {an}是等差数列,前n项和为Sn,且S2011/2011-S2009/2009=1,则公差d为? 设公差为d的等差数列{an}的前n项和为Sn,若a1=1,-2/17 等差数列｛a n｝中,前N项和为Sn,首项a1＝4,S9＝0,求公差d,若an+sn=－10,求n 在等差数列an中,前n项和为Sn,若Sm=2n,Sn=2m,则公差d的值为 设等差数列an的公差d为2,前n项和为Sn,则lim(an^2-n^2)/Sn=? 设数列{an}的前n项和为Sn,若{an}和{根号sn+n}都是公差为d的等差数列,则a1= 等差数列 an的前n项和为sn ,若s2=4,s4=20,则公差d= 设Sn为等差数列{an}的前n项和,S5=10,S10=-5,则公差d=? 等差数列｛an｝的前n项和为Sn,且S3=6,a3=4.求公差d=?