设等比数列{an}前n项和为Sn,若Sn=2,S2n=12,则S3n=?

设等比数列{an}前n项和为Sn,若Sn=2,S2n=12,则S3n=?
设等比数列{an}前n项和为Sn,若Sn=2,S2n=12,则S3n=?

设等比数列{an}前n项和为Sn,若Sn=2,S2n=12,则S3n=?
s2n/sn=a1q^(2n-1)/(a1q^(n-1))=q^n=2,同理s3n/s2n=qn=2,故s3n=48.

我看会做的人没有，别把分浪费了，给我吧，谢谢你啊

S3n=30