已知数列{an}中,a1=1,an+1=anan+3,(n∈N*)(1)求数列{an}的通项公式an,(2)若数列{bn}满足bn=(3

2025-05-12 13:26:53
推荐回答(1个)
回答(1):

(1)∵数列{an}中,a1=1,an+1=

an
an+3
,(n∈N*
1
an+1
an+3
an
=
3
an
+1

1
an+1
+
1
2
=3(
1
an
+
1
2
)

1
an+1
+
1
2
=(
1
a1
+
1
2
)?3n-1=
3n
2

∴an=
2
3n?1?1
.(4分)
(2)∵
2
3n?1?1
,bn=(3n-1)
n
2n
an
bn=(3n?1)?
n
2n
?
2
3n?1
=n?(
1
2
)n?1

Tn=1?1+2?(
1
2
)+3?(
1
2
)2+…+n?(
1
2
)n?1
,①
1
2
Tn=1?
1
2
+2?(