设数列{an}的各项均为正数,前n项和为Sn,已知4Sn=a2n+2an+1(n∈N*)(1)证明数列{an}是等差数列,并求

2025-04-21 18:58:11
推荐回答(1个)
回答(1):

(1)解:∵4Sn

a
+2an+1,
∴当n≥2时,4Sn?1
a
+2an?1+1

两式相减得4an
a
?
a
+2an?2an?1

∴(an+an-1)(an-an-1-2)=0
∵an>0,∴an-an-1=2,
4S1
a
+2a1+1
,∴a1=1
∴{an}是以a1=1为首项,d=2为公差的等差数列. 
∴an=a1+(n-1)d=2n-1;
(2)解:由(1)知Sn
(1+2n?1)n
2
n2

假设正整数k满足条件,
则(k22=[2(k+2048)-1]2
∴k2=2(k+2048)-1,
解得k=65;                         
(3)证明:由Snn2得:Smm2Skk2Spp2
于是
1
Sm
+
1
Sp
?
2
Sk
1
m2
+
1
p2
?
2
k2
k2(p2+m2)?2m2p2
m2p2k2

∵m、k、p∈N*,m+p=2k,
k2(p2+m2)?2m2p2
m2p