Can the Alternating Series Test Prove Divergence?

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Discussion Overview

The discussion centers on the question of whether the Alternating Series Test can be used to prove divergence, specifically in the context of the series \(\sum^{∞}_{n=1}(-1)^{n}\). Participants explore methods to demonstrate divergence through the behavior of the sequence of terms and the sequence of partial sums.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant notes that the Alternating Series Test is applicable for convergence but not necessarily for proving divergence.
  • Another participant suggests that proving the sequence of terms does not converge to 0 could demonstrate divergence.
  • There is a proposal to use the limit definition and look for an ε that leads to a contradiction as a method to prove divergence.
  • A participant recommends considering the Nth term test for divergence as a potential approach.
  • Another participant suggests showing that the sequence of partial sums does not converge as a straightforward method to establish divergence.

Areas of Agreement / Disagreement

Participants express varying approaches to proving divergence, with no consensus on a single method. Multiple competing views remain regarding the best strategy to demonstrate divergence.

Contextual Notes

Participants discuss the necessity of proving the sequence of terms does not converge to 0 and the behavior of partial sums, indicating potential limitations in their approaches.

Bipolarity
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Prove that [tex]\sum^{∞}_{n=1}(-1)^{n}[/tex] diverges.

I realized that the alternating series test can only be used for convergence and not necessarily for divergence. I might have to apply a ε-δ proof (Yikes!) which I have never been good at so please help me out.

BiP
 
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What about the sequence of terms?
 
Hmm good point. If we can prove the sequence does not converge to 0, we have proved that the series diverges. How can we do that? Shall I look at the limit definition and look for an ε that invokes a necessary contradiction?

BiP
 
Bipolarity said:
Hmm good point. If we can prove the sequence does not converge to 0, we have proved that the series diverges. How can we do that? Shall I look at the limit definition and look for an ε that invokes a necessary contradiction?

Yep, looks like a good plan. Try to do that.
 
Bipolarity said:
Hmm good point. If we can prove the sequence does not converge to 0, we have proved that the series diverges. How can we do that? Shall I look at the limit definition and look for an ε that invokes a necessary contradiction?
Look at the Nth term test for divergence.
 
Seems to me the simplest thing to do is to show that the sequence of "partial sums",
[itex]S_n= \sum_{i= 1}^n (-1)^n[/itex]
does not converge.
 

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