已知Sn是等差数列{an}的前n项和,a1=2009,S2009/2009-S2007/2007=-2,则S2009等于
设Sn是等差数列{an}的前n项和,已知a1=3,a2=11,则S7等于?
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是数列an的前n项和,已知a1=1,an=-Sn*Sn-1,(n大于等于2),则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
已知等差数列{an}中,a1=2,d=-2,前n项的和为 Sn,则 Sn( )
数列{an}是等差数列,已知a1=19,d=-2,Sn为{an}的前n项和
已知{an}为等差数列,a3=7,a1+a7=10,Sn为其前n项和,则使得Sn达到最大值的n等于( )
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=?
已知正项数列an的前n项和为Sn,a1=1,(an-2)²=8Sn-1.证明an是等差数列.
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?