Does the Limit of 1/(3+(-1)^n) Exist?

  • Context: Undergrad 
  • Thread starter Thread starter vabamyyr
  • Start date Start date
  • Tags Tags
    Limit
Click For Summary

Discussion Overview

The discussion revolves around the limit of the sequence defined by the expression 1/(3+(-1)^n) as n approaches infinity. Participants explore whether this limit exists, considering different cases for n being even or odd, and the implications of using real versus integer values.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant asserts that the limit does not exist, suggesting that the sequence yields different values for even and odd integers (1/4 for even n and 1/2 for odd n).
  • Another participant questions the clarity of the original post and introduces the concepts of lim sup and lim inf as tools to analyze the limit's existence.
  • A participant mentions that if n is considered as a real number, the expression becomes undefined due to the square root of negative numbers.
  • In response, another participant claims that the square root of negative numbers does exist, but is not real, indicating a potential misunderstanding of the definitions involved.
  • One participant references a proposition about subsequences of convergent sequences, suggesting a theoretical approach to the limit's behavior.

Areas of Agreement / Disagreement

Participants express differing opinions on the existence of the limit, with some arguing it does not exist while others introduce mathematical concepts that could support a different view. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

There are limitations regarding the definitions of convergence and the treatment of n as either an integer or a real number, which are not fully resolved in the discussion.

vabamyyr
Messages
65
Reaction score
0
I have a question:

what is lim (n--->infinity)= 1/(3+(-1)^n))? My opinion that this limit does not exist.
 
Physics news on Phys.org
"Do not opine, PROVE!"



Apocryphal quote from Euclid. :smile:
 
Are you asking about
[tex]\lim_{n\rightarrow\infty}\frac{1}{3+(-1)^n}[/tex]
perhaps? The equals sign in your post is confusing me. If so, are you familiar with the lim sup and lim inf? That would give you an easy direct proof: if lim sup = lim inf, that's the limit; otherwise, the limit does not exist.
 
i have dealt with sup but not with inf but i will look them up. Thx anyway.
 
manooch

vabamyyr said:
I have a question:

what is lim (n--->infinity)= 1/(3+(-1)^n))? My opinion that this limit does not exist.



if n∈Z (Z=Integer) then we have two answer for equation

1) if n=Even then answer=1/4

2) if n=Odd then answer=1/2

if n∈R (R=Real) then equation is undefined

for example: (-1)^1/2 does not exist.:smile:
 
manoochehr said:
for example: (-1)^1/2 does not exist.:smile:

It certainly does, it just isn't real.
 
I think you could use:

Proposition 4 Every subsequence of a convergent sequence converges to the same limit.
from: http://www.iwu.edu/~lstout/sequences/node3.html
 
thank you for help me
 
thank you for conduce:-p

Accordingly this sequence isn't convergent:smile:
 

Similar threads

  • · Replies 6 ·
Replies
6
Views
4K
  • · Replies 11 ·
Replies
11
Views
6K
  • · Replies 14 ·
Replies
14
Views
2K
  • · Replies 9 ·
Replies
9
Views
3K
  • · Replies 19 ·
Replies
19
Views
2K
  • · Replies 16 ·
Replies
16
Views
4K
  • · Replies 8 ·
Replies
8
Views
5K
  • · Replies 11 ·
Replies
11
Views
3K
  • · Replies 2 ·
Replies
2
Views
1K
  • · Replies 5 ·
Replies
5
Views
1K