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

设等差数列{an}的前n项和为Sn 若a1=Sn> 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 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 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 设Sn是等差数列{an}的前n项和,且S5S8,则a1 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 ①设an是等差数列,求证：{Sn/n}是等差数列②在等差数列an中,a1=-2010,其前n项和为Sn,若S2009/2009-S2007/2007= 设Sn是等差数列{an}的前n项和,且a1=7,S5=15. 设Sn是等差数列｛an｝的前n项和,已知a1=3,a2=11,则S7等于? 设数列{an}的前n项和为Sn,若{an}和{根号sn+n}都是公差为d的等差数列,则a1= 设等差数列｛an｝前n项和为Sn,若a1=-9,a3+a5=-6 设等差数列[an]的前n项和为Sn,若S9=72,则a1+a5+a9等于多少? 设公差为d的等差数列{an}的前n项和为Sn,若a1=1,-2/17 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? 设｛an｝是等差数列前n项和为Sn,若S4>=10,S5 设{an}是等差数列,a1=19.a21=3,数列{|an|}的前n项和为sn,求sn 设Sn为等差数列{An}的前n项和,求证：{Sn/n}是等差数列