己知各项均为正数的数列{an}满足:a1=3,且anan+12-2(an2-1)an+1-an=0,n∈N*.(1)设bn=an-1an,求数

2025-05-15 14:22:27
推荐回答(1个)
回答1:

(1)由题意知,
bn+1=an+1-

1
an+1
=
an+12?1
an+1
=
2(an2?1)
an
=2(an?
1
an
)
=2bn
b1a1?
1
a1
8
3

∴数列{bn}是公比为2,首项为
8
3
的等比数列,其通项公式为bn
2n+2
3

(2)由(1)有Sn+Tn=(a1?
1
a1
)2+(a2?
1
a2
)2
+…+(an?
1
an
)2
+2n
=(
23
3
2+(
24
3
2+…(
2n+2
3
2+2n
=
64
27
(4n?1)+2n
,n∈N*
为使Sn+Tn=
64
27
(4n?1)2+2n
,n∈N*,当且仅当
4n?1
27
为整数.
当n=1,2时,Sn+Tn不为整数,
当n≥3时,4n-1=(1+3)n-1=