已知等差数列an的前n项和为sn,若s6=2,s9=5,则s15=?要求用等差数列前n项和的公式解,
已知Sn是等比数列{An}的前N项和,S3,S9,S6成等差数列,则
已知等比数列{an}的公比为q,前n项和为Sn,且 S3,S9,S6 成等差数列,则q^3=( )
填空题等差数列{an}的前n项和为Sn,若S3=3,S6=9,则S9=( ).
已知等比数列{An}的公比为q,前n项的和为Sn,且S3,S9,S6成等差数列.
已知等比数列{An}的公比为q,前n项和为Sn,且S3,S9,S6成等差数列
已知Sn是首项为a的等比数列{an}的前n项和,S3,S9,S6成等差数列
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.
等比数列{an}的前n项和为sn,若S3,S9,S6成等差数列,求此数列的公差,
设等差数列[an]的前n项和为Sn,若a5=5a3,则S9/S5等于多少?
设等比数列an的前n项的和为Sn,若S6/S3=3,则S9/S6=
设Sn是等比数列{an}的前n项和,S3,S9,S6成等差数列.
1.设等比数列{an}的前n项和为Sn,若S6/S3=3,则S9/S6=?