I was wondering whether a sequence like[tex]x_n=n\sin

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Discussion Overview

The discussion revolves around the convergence or divergence of the sequence defined as \( x_n = n + \sin n \) and variations of it, particularly in the context of the extended real number system. Participants explore whether the sequence converges to infinity or diverges, considering oscillatory behavior and bounds.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that the sequence \( x_n = n + \sin n \) diverges but oscillates, proposing it converges to infinity in the extended real number system.
  • Another participant argues against the notion of convergence to infinity, stating that infinity is not a number and divergence is defined as not converging to a specific real point.
  • A participant agrees that the oscillatory nature of \( \sin n \) does not affect the divergence of the sequence, emphasizing that it diverges as it grows without bound.
  • Some participants assert that the sequence diverges or converges to infinity, citing that \( n + \sin n \) becomes arbitrarily large.
  • One participant introduces a modified sequence \( 0.5n + \sin n \) and questions its behavior, leading to further assertions that it still diverges.
  • Another participant notes that any positive coefficient in front of \( n \) will result in the sequence growing larger than \( \sin n \) as \( n \) increases.

Areas of Agreement / Disagreement

Participants express disagreement regarding the definition of convergence to infinity, with some asserting that the sequence diverges while others claim it converges to infinity in the extended real number system. The discussion remains unresolved with multiple competing views.

Contextual Notes

There are limitations regarding the definitions of convergence and divergence, particularly in the context of the extended real number system. The discussion also reflects uncertainty about the implications of oscillatory behavior on the overall divergence of the sequence.

dalcde
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I was wondering whether a sequence like
[tex]x_n=n\sin n[/tex]
converges* to infinity or diverges.

I'm pretty sure it goes to infinity but it still oscillates.

*Let's say we are in the extended real number system where we can converge to infinity

EDIT: I mean
[tex]x_n=n+\sin n[/tex]
 
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first of all there is no such thing as convergence to infinity
and infinity is not really a number
 


converges is it goes towards a certain value like a limit.

Yea i agree with daclde.

The sin n part will just oscillate from -1 to 0 to 1

So yea it diverges . No clue about extended real system but
 


Divergence doesn't really have points where it must diverge towards. Rather anything that doesn't converge to a specific real point is defined as divergent. Divergence towards infinity is just a popular saying for when something grows without bound. Just like oscillations, divergence towards infinity is not heading towards any definite point.

In the extended real system, this sequence is still divergent as it oscillates between positive and negative.
 


Sorry, I wanted to say
[tex]x_n=n+\sin n.[/tex]
Does it converge or diverge in this case?
 


dalcde said:
Sorry, I wanted to say
[tex]x_n=n+\sin n.[/tex]
Does it converge or diverge in this case?

This will diverge (or converge to infinity in the extended reals). the reason is that n+sin(n) becomes arbitrarily large. That is, we have

[tex]n-1\leq n+sin(n)[/tex]

and the sequence n-1 goes to infinity.
 


It converges to infinity in this case since n-1 is a lower bound.

edit: micromass explained it better
 


Sorry, what about
[tex]0.5n + \sin n[/tex]
since the previous sequence is actually always increasing?
 


it still diverges
 
  • #10


You can put any (positive) number you like in front of the "n". Eventually, n will be so large that even the product is far larger than sin(n).
 

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