已知等差数列an的前n项和为Sn,满足S8=20,且知首项与公差互为相反数,则a1=

(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项和为Sn,且满足an+2Sn*S(n-1)=0 (n>=2),a1=0.5.(1)求证：{1/Sn}是等差数列 （2）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 已知等差数列{an}的前n项和为Sn,满足关系lg(Sn+1)=n (n∈N*).试证明数列{an}为等比数列 已知数列｛an｝的前n项和为Sn,且满足an+2Sn×S(n-1)=0,a1=1/2.（1）求证：｛1/Sn｝是等差数列；（2）求数列｛an｝的通项公式. 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 已知等差数列an的前n项和为sn 且满足Sn=n²+n,则通项公式an=? 短时间内一定采纳,谢谢）已知数列{An}的前n项和为Sn且满足an=2S(n-1)Sn(n>=2),a1=1.已知数列{An}的前n项和为Sn且满足an=2S(n-1)Sn(n>=2),a1=1.(1)求证:{1/Sn}是等差数列(2)求an的表达式.(1)里是怎样做到 1/(sn) - 已知等差数列{an}满足a1=3.a4+a8=26,{an}的前n项和为Sn.求an及sn 已知等差数列{an}满足：a1=3,a4+a8=26,{an}的前n项和为Sn,求an及Sn,在线等啊, 已知等差数列{an}满足:a3=7,a1＋a11=26,{an}的前n项和为Sn,求an及Sn 已知等差数列an的前n项和为Sn,且满足a2+a4=14,S7=70 求证等差数列!已知数列an的各项均为正数,前n项和为Sn,且满足2Sn=a∧2n+n-4 在等差数列{an}的前n项和为Sn,已知Sn=S(19-n)则当|an|最小时,n=___ Sn为等差数列an的前n项和S'n为等差数列Sn为等差数列{an}的前n项和S‘n为等差数列{bn}de前n项和,已知Sn:S’n=（7n+1）:（4n+27）,求a11:b11的值 已知数列an的前n项为Sn,且满足Sn=S(n-1)/2S(n-1)+1(n≥2）,a1=2(1)求证:{1/Sn}是等差数列(2)求an的表达式. 等差数列{an}的前n项和为Sn,已知S6=36,Sn=324,S(n-6)=144(n>6),则n为多少? 已知{an}是首项为19,公差为-2的等差数列,Sn为{An}的前n项和,求通项a、b及前n项和S