已知{an}是等差数列 求证Sn,S2n-Sn,S3n-S2n成等差数列

已知{an}是等差数列 求证Sn,S2n-Sn,S3n-S2n成等差数列 已知an是等差数列,前n项和为Sn,求证:S3n=3(S2n-Sn) 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 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 已知{an}是等差数列,若Sn=20,S2n=38,求S3n的值 等差数列{an}前n项和为sn,求证S2n-1=(2n-1)an 等差数列前n项和为Sn,求证:S2n-1=(2n-1)an 已知数列{an}是各项均不为0的等差数列,前n项和为Sn,且(an)^2=S2n-1,求an 已知等差数列{an} 若Sn=a S2n=b 求S3n 在等差数列(an)中,已知Sn=30,S2n-100,则S3n= 已知数列{An},Sn=0.125（An+2)(An+2).求证：{An}是等差数列 若an是等差数列,则Sn,S2n-Sn,S3n-S2n,…也成等差数列,求公差公差为dn^2 求证明过程 详细点 等差数列（an）中,Sn=30,S2n=100,则S3n= 为什么Sn S2n-Sn S等差数列（an）中,Sn=30,S2n=100,则S3n= 为什么Sn S2n-Sn S3n-S2n成等差数列 已知数列{an}满足a1=3,(an+1)-3an=3^n(n,n∈N*),数列{bn}满足bn=3^(-n)an求证：数列{bn}是等差数列设sn=(a1)/3+(a2)/4+(a3)/5+.(an)/(n+2),求满足1、128<sn/s2n<1/4的所有正整数n的值 已知数列{an}为等差数列,前n项为Sn,且Sn=25,S2n=100,那么S3n等于 (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 已知等差数列{An}的前N项和为Sn 且S4/S8=1/3 则S8/S16=?A 3/10 B 1/3 C 1/9 D 1/8不用公式进行计算，因为等差数列有个规律：Sn，S2n-Sn，S3n-S2n。是等差数列