已知2Sn=a^2n+n-4求证：an为等差数列.并求出{an}的通项公式

已知2Sn=a^2n+n-4求证：an为等差数列.并求出{an}的通项公式 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 已知an=n/(n+1),bn=an+1/an,bn的前n项和为Sn求证：2n＜Sn＜2n+1 设数列的前n项和为Sn,已知a1=1,an+1=(n+2/n)*Sn,(n=1,2,3,...) 1,求证Sn/n是等比数列 2,Sn+1=4an 已知an=2^n-1/2^n,记数列{1/an}的前n项和为Sn,求证Sn<4/3. 已知数列an的前n项和为sn sn=2-an求证an是等比数列主要怎么求证a=1≠0? 已知数列an,若a1=1,nan+1=(n+2)Sn,求证Sn/n为等比数列已知数列an,若a1=1,nan+1=(n+2)Sn,求证数列Sn/n为等比数列,并且求Sn 已知数列{an}满足a1=1,a2=4,a(n+2)+2an=3a(n+1),（n∈N*）1）求证{a(n+1)-an}是等比数列,并求数列{an}的通项公式2）记数列{an}的前n项和为Sn,求使得Sn>21-2n成立的最小整数n 数列an的前n项为sn,已知2an-2^n=sn.求证an-n·2^(n-1)是等比数列 设数列An的前n项和为Sn,已知a(1)+2a(2)+3a(3)+…+na(n)=(n-1)Sn+2n(n为正整数）.求证数列Sn+2是等比数列 已知数列{an}的前n项和为Sn,a1=1,a（n+1）=1+2Sn.设bn=n/an,求证:数列{bn}的前n项和Tn＜9/4 已知等比数列前n项和为Sn,a1a2a3...a*n=Pn,1/a1+1/a2+1/a3+...+1/an.求证：（Pn)^2=(Sn/Tn)^n 已知数列{an}的前N项和为Sn 且an+1=Sn-n+3,a1=2,设Bn=n/Sn-n+2前N项和为Tn 求证Tn 小于4/3 (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=n^2-3n,求证：数列{an}是等差数列 已知数列{an}的前n项和Sn=-n^2+18n,求证:{an}为等差数列 已知数列｛an｝前n项和为Sn,对于n属于自然数,总有Sn=(a1+an)n/2,求证｛an｝为等差数列. 已知数列an中,a1=2,an+1=4an-3n+1,求证数列{an-n}为等比数列设{an}的前n项和Sn,求S（n-1）-4Sn的最大值