在由正数组成的等比数列{an}中,若a3a4a5=3π,则sin(log3a1+log3a2+…+log3a7)的值为(  ) A.12 B.32 C.1 D.-32

问题描述:

在由正数组成的等比数列{an}中,若a3a4a5=3π,则sin(log3a1+log3a2+…+log3a7)的值为(  )
A.

1
2

B.
3
2

C. 1
D. -
3
2

因为由正数组成的等比数列{an}中,a3a4a5=3π,所以a43=3π,a4=3

π
3

∴log3a1+log3a2+…+log3a7
=
log (a1•a2a3 •a4• a5a6a7)3

=
log
a 74
3

=7
log
a  4
3

=7
log 3
π
3
3

=
3

∴sin(log3a1+log3a2+…+log3a7
=sin
3

=sin(2π+
π
3

=sin
π
3

=
3
2

故选B.