等差数列an的前n项和Sn,S5=5,S10=15,则S15=

设Sn是等差数列an的前n项和,若S5/S3=5/9,则S9/S5= 等差数列{an}的前n项和为Sn,且S10-S5=3,S15=? 设等差数列an的前n项和为Sn,若S4>=10,S5 设等差数列an,的前n项和为Sn,a2+a4=6,求S5 已知Sn表示等差数列an的前n项和且S5/S10=1/3 求S5/S20=? 设等差数列{an}的前n项和为Sn,且S5=-5,S10=15,求数列{Sn/n}的前n项和Tn 等差数列{an}的前n项和为Sn,且S5=-5,S10=15,求数列{Sn/n}的前n项和T 递减等差数列｛an}的前n项和sn满足：s5=s10,则要sn最大,n等于多少? 等差数列{an}的前n项和为Sn,且6S5-5S3=5,则a4= 等差数列{an}的前n项和为Sn,且6S5-5S3=5,则a4= 等差数列{an}的前n项和为Sn,且6S5-5S3=5,则a4=______. 设等差数列｛AN｝的前N项和为SN,6S5-5S3=5则A4=? 等差数列{an}的前n项和为Sn,且6S5-5S3=5,则a4= 设Sn为等差数列{an}的前n项和,S5=10,S10=-5,则公差d=? 等差数列an的前n项和Sn,S5=5,S10=15,则S15= 设Sn是等差数列an的前n项和,a5=5a3,则S9/S5=? 设等差数列{An}的前n项和为Sn,若A5=5A3,则S9/S5=? 设Sn是等差数列an的前n项和,若a5/a3=5/9,则S9/S5=