社无穷等差数列an的前n项和为Sn,若不等式an^2+Sn^2/n^2>=t/5a1^2
设数列an的前n项和为Sn,a1=1,an=(Sn/n)+2(n-1)(n∈N*) 求证:数列an为等差数列,
等差数列{An}的前n项和为Sn,若 lim Sn/n方 =2
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.
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
设数列an的前n项和为sn,对于所有的自然数n都有sn=n(a1+an)/2,求证an是等差数列
已知等差数列{an}的前N项和为Sn,a1=-2/3,满足Sn+1/Sn+2=an(n大于等于2)
已知等差数列{an}的前N项和为Sn,a1=-2/3,满足Sn+1/Sn+2=an(n大于等于2),
设Sn为等差数列{an}的前n项和,若a1=1,公差d=2,Sn+2-Sn=36,则n=( )
已知等差数列{an}中,a1=2,d=-2,前n项的和为 Sn,则 Sn( )
已知等差数列an中a1=2,其前n项和sn,若数列{Sn/n}构成一个公差为2的等差数列,则a3=?
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