已知{an}是等差数列,前n项和是Sn,且a2+a7=9,S6=7a3.1）求数列{an}的通项公式.2) 令bn=an*2^an,求bn前n项和Tn.3）令Cn=an*a(n+2),求数列1/Cn前n项和Gn

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 (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}的前n项和sn满足sn=an^2+bn,求证{an}是等差数列 设Sn为等差数列{An}的前n项和,求证：{Sn/n}是等差数列 已知等差数列{an}的前n项和是sn=32n一n*n,求{|an|}的前n项和sn 已知等差数列{an}中,Sn是它的前n项和,若S16>0,S17 等差数列an的前n项和是sn,已知s14>0,s15 等差数列{an}的前n项和是Sn,已知S14>0,S15 已知等差数列{an}中,Sn是它的前n项和,若S16>0,S17 已知数列{an}的前n项和为Sn=n^2-3n,求证：数列{an}是等差数列 已知数列{an}的前n项和Sn=100n-n^2,证明{an}是等差数列 已知数列｛an｝的前n项和sn=n方+3n,求证数列{an}是等差数列 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? 已知数列{an}的前n项和为Sn,且满足an+2Sn*Sn-1=0,a1=1/2.求证：{1/Sn}是等差数列 已知数列an是等差数列,且a1不等于0,Sn为这个数列的前n项和,求limnan/Sn.limSn+Sn-1/Sn+Sn-1 已知等差数列的前n项和An=n^2-17n.即便Sn最小的n值是 已知数列{An}的前N项和Sn=4n2+3n,求证{An}是等差数列