各项均为正数的数列{an}中,a1=1,Sn是数列{an}的前n项和,对任意n∈N*,有2Sn=2an2+an-1.(1)求数列{a

2025-05-14 06:44:13
推荐回答(1个)
回答1:

(1)∵2Sn=2an2+an-1,∴2Sn+1=2an+12+an+1-1,
两式相减得:2an+1=2(an+1-an)(an+1+an)+(an+1-an),
即(an+1+an)(2an+1-2an-1)=0.
∵an>0,∴2an+1-2an-1=0,∴an+1-an=

1
2

∴数列{an}是以1为首项,
1
2
为公差的等差数列,
∴an=
n+1
2

(2)∵bn=
an
2n
=
n+1
2n+1

∴Tn=
2
22
+
3
23
+
4
24
+…+
n+1
2n+1
,①
1
2
Tn=
2
23
+
3
24
+
4
25
+…+
n+1
2n+2
,②
①-②得
1
2
Tn=
1
2
+
1
23
+
1
24
+…+
1
2n+1
-
n+1
2n+2

=
1
2
+
1
8
(1?
1
2n?1
)
1?
1
2
?
n+1
2n+2

=
3
4
-
1
2n+1
-
n+1
2n+2

∴Tn=
3
2
-
1
2n
-
n+1
2n+1
=
3
2
-
n+3
2n+1