已知等差数列｛An｝中,Sn是它前n项和,设A4=-2,S5=-20.求数列｛an｝的通项公式?

已知等差数列{an}中,Sn是它的前n项和,若S16>0,S17 已知等差数列{an}中,Sn是它的前n项和,若S16>0,S17 已知等差数列{an}中Sn是它的前n项和,设a6=2,S10=10 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 已知数列{an}中,a2=2,前n项和为Sn,且Sn=n(an+1)/2证明数列{an+1-an}是等差数列 已知等差数列｛An｝中,Sn是它前n项和,设A4=-2,S5=-20.求数列｛an｝的通项公式? 等差数列中,已知前n项和Sn=5n^2+3n,则通项an? 已知an是等差数列,前n项和为Sn,求证:S3n=3(S2n-Sn) {an}是等差数列前n项和Sn已知Sm=a Sn-Sn-m=b 求Sn 等差数列{an}中,Sn是{an}前n项和,已知S6=2,S9=5,则S15= 等差数列{an}中,Sn是{an}前n项和,已知S6=2,S9=5,则S15= 已知等差数列{an}中a1=31,Sn是它的前n项,S10=S22. (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 已知数列{an}中,an>0,前n项和为Sn,且满足Sn=1/8(an+2)^2.求证数列{an}是等差数列. 已知等差数列an中,前n项和sn=n^2-15n,则使sn为最小值的n 在等差数列{an}中,已知Sn,S2n,S3n分别表示数列的前n项和,前2n项和,前3n项和.求证:Sn,S2n-Sn,S3n-S2n是等差数列 已知数列{an}的前n项和sn满足sn=an^2+bn,求证{an}是等差数列