已知{an}为等差数列,Sn为其前n项喝,且2Sn=an+2n²(1)求an.Sn

来源：学生作业帮编辑：作业帮分类：数学作业时间：2024/08/26 22:05:46

2a(1)=2s(1)=a(1)+2,a(1)=s(1)=2,
2s(n)=a(n)+2n^2,
2s(n+1)=a(n+1)+2(n+1)^2,
2a(n+1)=2s(n+1)-2s(n)=a(n+1)-a(n) + 2(2n+1),
a(n+1) = - a(n) + 4n + 2,
a(n+1) - 2(n+1) = -a(n) + 2n = -[a(n)-2n],
{a(n)-2n}是首项为a(1)-2=0,公比为（-1）的等比数列.
a(n)-2n = 0*(-1)^(n-1) = 0,
a(n) = 2n,
2s(n) = a(n) + 2n^2 = 2n + 2n^2 = 2n(n+1),
s(n) = n(n+1).

已知等差数列｛an｝的前n项和为Sn,且a1不等于0,求（n*an)/Sn的极限、（Sn+Sn+1）/(Sn+Sn-1) 已知等差数列{an}的前n项和为Sn,且(2n-1)Sn+1 -(2n+1)Sn=4n²-1(n∈N*) 已知数列An中,其前n项和为Sn,A1=1,且An+1=2Sn,求An的通项公式和Sn 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}的前n项和为Sn,且满足Sn=Sn-1/2Sn-1 +1,a1=2,求证{1/Sn}是等差数列数列{an}前n项和为Sn,且2Sn+1=3an,求an及Sn 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}是等差数列已知数列{an}为等差数列,其前n项和为Sn,且a5=8,S5=20 (1)求Sn;(2)若... 已知数列｛An｝的各项均为正数,前n项和为Sn,且满足2Sn=An²+n-4 1.求证｛An｝为等差数列已知数列{an}a1=2前n项和为Sn 且满足Sn Sn-1=3an 求数列{an}的通项公式an 已知数列an是等差数列,且a1≠0,Sn为这个数列的前n项和.求1、lim nan/Sn 2、lim (Sn+Sn+1) 已知数列an其前n项和为Sn,且Sn=3n^2+5n,求证数列an是等差数列