When n= 1,/s1=1a1=1(1+1) =/kloc-.
a 1=2
When n≥2,
1/S 1+ 1/S2+...+ 1/Sn = n/(n+ 1)( 1)
1/s1+1/S2+...+1/sec (n- 1)=(n- 1)/n (2)
( 1)-(2)
1/Sn = n/(n+ 1)-(n- 1)/n =[n? -(n+ 1)(n- 1)]/[n(n+ 1)]=(n? -n? + 1)/[n(n+ 1)]= 1/(n? +n)
Sn=n? +n
S(n- 1)=(n- 1)? +(n- 1)
an=Sn-S(n- 1)=n? +n-(n- 1)? -(n- 1)=2n
When n= 1, a 1=2, which also satisfies the general formula.
The general formula of sequence {an} is an=2n.
bn=( 1/2)^(an)=( 1/2)(2n)= 1/4?
b 1 = 1/4 b(n+ 1)/bn=( 1/4)^(n+ 1)/( 1/4? )= 1/4
Sequence {bn} is a geometric series with 1/4 as the first term and 1/4 as the common ratio.
b 1+b2+...+bn =( 1/4)( 1- 1/4? )/( 1- 1/4)=( 1/3)( 1- 1/4? )
n≥ 1,0 & lt; 1/4? ≤ 1/4 3/4≤ 1- 1/4? & lt 1 1/4≤( 1/3)( 1- 1/4? )& lt 1/3
1/m & lt; 1/4 m? -6m + 16/3≥ 1/3
1/m & lt; 1/4m & lt; 0 or m> four
m? -6m + 16/3≥ 1/3
m? -6m +5≥0
(m-5)(m- 1)≥0
M≥5 or m≤ 1
To sum up, m is obtained.