Sn是等差数列{an}的前n项和,S7=3(a3+a7),那么S9/a4=?

来源：学生作业帮助网编辑：六六作业网时间：2024/12/23 11:07:32

Sn是等差数列{an}的前n项和,S7=3(a3+a7),那么S9/a4=?Sn是等差数列{an}的前n项和,S7=3(a3+a7),那么S9/a4=?Sn是等差数列{an}的前n项和,S7=3(a3

Sn是等差数列{an}的前n项和,S7=3(a3+a7),那么S9/a4=?
Sn是等差数列{an}的前n项和,S7=3(a3+a7),那么S9/a4=?

Sn是等差数列{an}的前n项和,S7=3(a3+a7),那么S9/a4=?
s7=(a1+a7)*7/2=3(a3+a7)
所以7(a1+a1+6d)=6(a1+2d+a1+6d)
所以a1=3d
s9/a4
=[(a1+a9)*9/2]/a4
=(a1+a1+8d)*9/[2(a1+3d)]
=14d*9/12d
=21/2

设Sn是等差数列an的前n项和,若S3/S7=1/3,则S6/S7= {an}是等差数列,前n项和为Sn,若a3=18-a4,求S7 等差数列｛an｝的前n项和为Sn,则(S7-S3)/S10=? 已知等差数列{an}的前n项和为Sn,则S7-S3除以S10= 等差数列an的前n项和为sn 且s7=7 则a2+a6 设Sn是等差数列 an 的前n项和,S7=3(a3+a7),求a5/a4的值设Sn是等差数列{an}的前n项和,已知a2=3,a6=11,则S7=? 设Sn是等差数列｛an｝的前n项和,已知a2=3,S11=121,则S7= 设Sn是等差数列｛an｝的前n项和,若S7=35,则a4= 有人吗设Sn是等差数列an的前n项和,已知a2=3,S11=121,则S7等于 Sn是等差数列{an}的前n项和,S7=3(a3+a7),那么S9/a4=? 设Sn是等差数列an的前n项和,若S3/S6=1/3,则S6/S7=? 设Sn是等差数列[an}的前n项和,若S7=5,则a4= 设Sn是等差数列｛an｝的前n项和,已知a1=3,a2=11,则S7等于? 设Sn是等差数列 an 的前n 项和,已知a2=3,a6=11,求S7. 设Sn是等差数列｛an｝的前n项和,已知a2=3,a6=11,则S7等于? 设Sn是等差数列{an}的前N项和,若S7=35,则a4为几? {an}是等差数列 S7=7 S15=75 Tn是数列{Sn/n}的前n和求Tn