Can the Convergence of a Sequence be Proven by Using Epsilon and Inequalities?

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Homework Help Overview

The discussion revolves around the convergence of a sequence \( a_n \) given that a related sequence \( b_n = pa_n + qa_{n+1} \) is convergent, with the condition that \( |p| < q \). Participants are exploring how this condition affects the convergence of \( a_n \) and are seeking insights into the implications of the inequality.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants are attempting to understand the relationship between the convergence of \( b_n \) and \( a_n \), questioning the significance of the inequality \( |p| < q \). Some have considered counterexamples to illustrate potential pitfalls when the inequality does not hold. Others are exploring the use of the epsilon definition of convergence.

Discussion Status

The discussion is ongoing, with participants sharing their thoughts on the implications of the inequality and the challenges they face in proving the convergence of \( a_n \). There is a recognition of the need for a deeper understanding of the conditions provided, and some guidance has been offered regarding the epsilon definition.

Contextual Notes

Participants have noted difficulties in proving the theorem and are grappling with the intuitive understanding of the inequality \( |p| < q \). There is an acknowledgment of the limitations posed by the problem's setup and the need for further clarification on the definitions involved.

sebasvargasl
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Hello Physics Forums community! I've been struggling for a while with this one
emoticon-0121-angry.gif
; so basically a sequence a_n is given to us such that the sequence b_n defined by b_n = pa_n + qa_(n+1) is convergent where abs(p)<q. I need to prove a_n is convergent also. Any hint would be of so much help, thank you.

(I've tried proving it is Cauchy but no insight ever comes, just messing with inequalities. I haven't fully understood the role played by abs(p)<q)
 
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sebasvargasl said:
Hello Physics Forums community! I've been struggling for a while with this one
emoticon-0121-angry.gif
; so basically a sequence a_n is given to us such that the sequence b_n defined by b_n = pa_n + qa_(n+1) is convergent where abs(p)<q. I need to prove a_n is convergent also. Any hint would be of so much help, thank you.

(I've tried proving it is Cauchy but no insight ever comes, just messing with inequalities. I haven't fully understood the role played by abs(p)<q)

You can start by trying to think what could go wrong if ##|p|<q## isn't true. Suppose ##a_n=(-1)^n## and ##p=1## and ##q=1##.
 
I'm well aware of the counter examples when the inequality doesn't hold. I just can't find a way to prove the theorem; and to do this I need to fully understand the importance of the inequality. I can't see it intuitively
 
You can use the definition in terms of epsilon.
 

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