等比数列an的前N项和为Sn,a3=-12,S3=-9,求公比q和S5

等比数列{an}的前n项和为Sn,已知S1,S3,S2成等差数列1 ,求｛an｝的公比q2 ,若a1-a3=3求Sn 设数列an的前n项和为Sn,且2an=Sn+2n+1 求a1 a2 a3 求证:数列{an+2}是等比数列 求数列{n*an}的前n项和Tn 设数列an的前n项和为Sn,且2an=Sn+2n+1 求a1 a2 a3 求证:数列{an+2}是等比数列 求数列{n*an}的前n项和Tn 设等比数列{an}的公比为q=2,前n项和为{Sn},求S4/a3的值 an是公比为正数的等比数列,a1=2 a3=a2+4 求数列{(2n+1)an}的前n项和sn 等比数列an的前N项和为Sn,a3=-12,S3=-9,求公比q和S5 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=?思路,本人基础不好 记等差数列an的前n项和为Sn,设S3=12,且2a1,a2,a3+1成等比数列,求Sn 记等差数列{an}的前n项和为Sn,设S3=12,且2a1、a2、a3+1成等比数列,求Sn 记等差数列{an}的前n项和为Sn.设S3=12,且2a1,a2,a3+1成等比数列,求Sn 等差数列｛an｝的前n项和为Sn,设S3=12,且2a1,a2,a3 1成等比数列,求Sn? 等差数列an的前n项和为Sn,设S3=122,且2a1.a2.,a3+1成等比数列,求Sn 设数列{an}前n项和为Sn,已知a1+2a2+3a3+...+nan=(n-1)Sn+2n,（1）求a2,a3的值；（2）求证：数列{Sn+2}是等比数列. 已知等比数列{an}的前n项和为Sn,且a3=2,S3=3/2,求a6 等比数列{an}的前n项和为Sn,若4S3-3a3=0公比q=? 设sn为等比数列an的前n项和,2a3-a4=0,S5/a1= 等比数列an sn是前n项的和,s3=3a3.求公比. Sn为等比数列{an}前n项和,an=(2n-1)*3的n次方,求Sn