设等比数列{an}的前n项和为Sn,若S6S3=3,则S9S6=(  ) A.12 B.73 C.83 D.1

问题描述:

设等比数列{an}的前n项和为Sn,若

S6
S3
=3,则
S9
S6
=(  )
A.
1
2

B.
7
3

C.
8
3

D. 1

S6
S3
=3,
a1(1−q6)
1−q
a1(1−q3)
1−q
=3
 整理得,1+q3=2,
∴q3=2
S9
S6
= 
a1(1−q9)
1−q
a1(1−q6)
1−q
=
7
3

故选B.