设Sn是等差数列{an}的前n项和,a12=-8,S9=-9,﹛Sn/n﹜是等差数列,求﹛Sn/n﹜的前n项的和
设Sn是等差数列{an}的前n项和,a12=-8,S9=-9,﹛Sn/n﹜是等差数列,求﹛Sn/n﹜的前n项的和
Sn是等差数列An的前N项和.A12=-8,S9=-9,则S16=多少
设Sn是等差数列{an}的前n项和,a12=-8,S9=-9,则S16=______.
设Sn是等比数列{an}的前n项和,S3,S9,S6成等差数列.
设Sn是等差数列{an}的前n项和,若a5/a3=5/9,则S9/S5=:
设Sn是等差数列an的前n项和,a5=2,an-4=30(n≥5,n∈N*),Sn=136,求n
设Sn为等差数列的前n项和,且S9=18,Sn=240,若an-4=30求项数n
已知Sn是等比数列{An}的前N项和,S3,S9,S6成等差数列,则
设等差数列 {an}的前n 项和为Sn,若S9>0 ,S10
设Sn是等差数列的{an}前n项和,且S9=18,Sn=240,若an-4=30(n>9),则n的值为( )
已知Sn是等比数列{an}的前n项和,设公比为q,且S3,S9,S6成等差数列.
设等差数列{an}的前n项和为Sn,且a5=3a7,则S9/S13=?