问题 解答题
已知等比数列{an}各项均为正数,且2a1+3a2=8,a32=
1
4
a2a6

(1)求数列{an}的前n项和Sn
(2)若数列{bn}满足bn=
1
log2(Sn+1).log2(Sn+1+1)
(n∈N*)
,求数列{bn}的前n项和Tn
答案

(1)∵正项等比数列{an}中,a32=

1
4
a2•a6=
1
4
a42

∴q2=

a42
a32
=4,q>0,

∴q=2;

又2a1+3a2=8,即2a1+3a1q=8,

∴a1=1.

∴Sn=

1×(1-2n)
1-2
=2n-1.

(2)∵bn=

1
log2(Sn+1).log2(Sn+1+1)

=

1
log2(2n-1+1).log2(2n+1-1+1)

=

1
log22nlog22n+1

=

1
n(n+1)

=

1
n
-
1
n+1

∴Tn=b1+b2+…+bn

=(1-

1
2
)+(
1
2
-
1
3
)+…+(
1
n
-
1
n+1

=1-

1
n+1

=

n
n+1

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