等差数列{an}的前n项和是Sn,若a1+a2=5,a3+a4=9,则S10的值为多少

设等差数列{an}的前n项和为Sn 若a1=Sn> 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? 等差数列｛an｝3a4=7a7,且a1>0sn是等差数列｛an｝的前n项和,若sn取最大值, 设数列{an}的前n项和为Sn,若对任意正整数,都有Sn=n(a1+an)/2,证明{an}是等差数列. 设Sn是等差数列{an}的前n项和,且S5S8,则a1 设数列｛an｝的前n项和为sn,若对于所有的正整数n,都有sn=n（a1+an）/2,证明｛an｝是等差数列设数列｛an｝的前n项和为sn,若对于所有的正整数n,都有sn=n（a1+an）/2,证明｛an｝是等差数列 等比数列{an}中若a1=1,且前N项和SN构成等差数列,则等差数列{sn}的公差是?且前N项和SN构成等差数列,这句怎么理解..请详细给出解题思路3Q 已知Sn是等比数列an的前n项和,S4S10S7成等差数列,若a1=1,求数列an^3的前n项的积 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 设Sn是等差数列{an}的前n项和,若公差d=-3/23.a1>0,则使Sn取最小值的正整数n的值是 {an}是等差数列,a1不等于0,Sn是它前n项的和.求lim (n→∞) (Sn+S(n+1))/(Sn+S(n-1)) 设Sn为等差数列{An}的前n项和,求证：{Sn/n}是等差数列 设Sn是等差数列an前n项和,若a1=-11,a3+a7=-6求当Sn取最小值时n的值 数列前n项和为sn,a1=1,an+sn是公差为2的等差数列,求an-2是等比数列,并求sn 等差数列的证明问题已知数列{an}的前n项和Sn=n(a1+an)/2，求证数列{an}是等差数列。 一道等差数列的题!已知Sn是等差数列{An}的前n项和,a1>0,S3=S10,当n为何值时,Sn有最大值? 设sn是等差数列an的前n项和,若a1=-16,公差为2,sn最小值是第几项请详解