若{an}是公差d≠0等差数列,{bn}是公比q≠1等比数列,已知a1=b1=1,且a2=b2,a6=b3.(1)求数列{an}和{b

2025-05-16 16:55:34
推荐回答(1个)
回答1:

(1)依题得

1+d=q
1+5d=q2
?
d=3
q=4

∴an=3n-2,bn=4n-1
(2)∵
1
anan+1
=
1
(3n?2)(3n+1)
=
1
3
1
3n?2
-
1
3n+1
),
∴Sn=
1
3
[(
1
1
-
1
4
)+(
1
4
-
1
7
)+…+(
1
3n?2
-
1
3n+1
)]
=
n
3n+1

(3)假设存在常数a,b满足题意,把an=3n-2,bn=4n-1代入an=logabn+b,
得:3n-2=loga4n?1+b,
即(3-loga4)n+(loga4-b-2)=0对一切n∈N*都成立,
3?loga4=0
loga4?b?2=0

解得:
a=
3 4
b=1

即存在常数a=
3 4
,b=1满足题设.