设数列{an}的前n项和为Sn,已知a1=1,且an+2SnSn-1=0(n≥2),(1)求数列{Sn}的通项公式;(2)设Sn=1f

2025-05-12 18:49:03
推荐回答(1个)
回答1:

解答:(1)解:∵an+2SnSn-1=0(n≥2),
∴Sn-Sn-1+2SnSn-1=0.---------(3分)

1
Sn
-
1
Sn?1
=2.
又∵a1=1,---------------(5分)
∴Sn=
1
2n?1
(n∈N+).---------------(7分)
(2)证明:∵Sn=
1
f(n)
,∴f(n)=2n-1.--------------------------(8分)
∴bn=2(
1
2n
)-1+1=(
1
2
n-1.---------------------------------------(9分)
Tn=(
1
2
0?(
1
2
1+(
1
2
1?(
1
2
2+…+(
1
2
n-1?(
1
2
n=(
1
2
1+(
1
2
3+(
1
2
5+…+(
1
2
2n-1
=
2
3
[1-(
1
4
n].-------------------------------------------------------(11分)
∴Pn=
1
1×3
+
1
3×5
+…+
1
(2n?1)(2n+1)
---------------(13分)
=
1
2
(1?
1
3
+
1
3
?
1
5
+…+
1
2n?1
?
1
2n+1
)
=
1
2
(1?
1
2n+1
)
-------------------------------(14分)