sn表示等差数列an的前n项和,且s4=s9 a1=-12
Sn表示等差数列{an}的前n项的和,且S4=S9,a1=-12
设等差数列{an}的前n项和为Sn,已知a4=12,且S8>0,S9
等差数列{an}中,a1>0,前n项和为Sn,且S9>0,S10
设等差数列an的前n项和为Sn,a1=3/2,且s1,s2,s4成等比数列,求sn
等比数列{an}的前n项和为Sn,且4a1,2a2,a3成等差数列.若a1=1,则S4=( )
等比数列{an}的前n项和为Sn,且4a1,2a3,a3成等差数列,若a1=1,则S4=?
已知等差数列an的前n项和为Sn,且a1+a3=10,S4=24.1求数列an的通项公式
设Sn为等差数列{an}的前n项和,S4=14,S10-S7=30,则S9=______.
设等差数列{an}的前n项和为Sn,且a5=3a7,则S9/S13=?
已知等差数列{an}的首项a1=a,公差d=2,前n项和为Sn,且S1,S2,S4成等比数列
{An}为等差数列,前n项和为Sn,且S4=-62,S6=-75,求|a1|+|a2|+…+|a14|的值. 解:设Ak
等比数列的前n项和为Sn,a1为3/2,且S3,S5,S4成等差数列,求an