等比数列{an}的前n项和为Sn,若S3+3S2=0,则公比q=____.
-2。当q=1时,S3=3a1,S2=2a1,由S3+3S2=0得,9a1=0,所以a1=0与{an}是等比数列矛盾,故q≠1,由S3+3S2=0得[a1(1-q3)/(1-q)]+[3a1(1-q2)/(1-q)]=0,解得q=-2.
等比数列{an}的前n项和为Sn,若S3+3S2=0,则公比q=____.
-2。当q=1时,S3=3a1,S2=2a1,由S3+3S2=0得,9a1=0,所以a1=0与{an}是等比数列矛盾,故q≠1,由S3+3S2=0得[a1(1-q3)/(1-q)]+[3a1(1-q2)/(1-q)]=0,解得q=-2.