Does the Series Sum of 1 + (-1)^n/n Converge?

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SUMMARY

The series sum of 1 + (-1)^n/n converges conditionally, as established by the alternating series test. The series can be separated into two components: Σ1, which diverges, and Σ(-1)^n/n, which converges. The confusion arises from the interaction between these two series, where the divergent series does not negate the convergence of the alternating series. Thus, the overall series converges conditionally despite the presence of a divergent component.

PREREQUISITES
  • Understanding of series convergence tests, specifically the alternating series test.
  • Familiarity with the concept of conditional convergence versus absolute convergence.
  • Basic knowledge of limits and their role in determining convergence.
  • Ability to manipulate and analyze infinite series notation.
NEXT STEPS
  • Study the Alternating Series Test in detail to understand its application and limitations.
  • Learn about conditional versus absolute convergence in series.
  • Explore the Limit Comparison Test and its role in series convergence.
  • Investigate the implications of divergent series on the convergence of combined series.
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Students studying calculus, particularly those focusing on series and convergence, as well as educators seeking to clarify concepts related to series convergence tests.

That Neuron
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Homework Statement



The problem contained five answer choices, of which I the answerer was to find one that fit the criteria of the question. The question was: "Which series of the following terms would be convergent?".

It listed five series, The answer was this term: 1 + (-1)n / n.

Homework Equations



[itex]\Sigma[/itex]1 + (-1)n / n.

The Attempt at a Solution



I find this very confusing simply because whilst separating the series into two separate series, [itex]\Sigma[/itex]1 and [itex]\Sigma[/itex](-1)n / n, The second series converges (yes I was surprised also) by the alternating series test. Originally, I was dumbfounded because of the absolute value test, so I suppose the series is conditionally convergent. Anyways, if [itex]\Sigma[/itex](-1)n / n is convergent and [itex]\Sigma[/itex]1 is divergent, 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1... + 1 ... +1 (you get the point) Then how can a finite number (the second alternating series) affect convergence? Also, the limit test kind of rules convergence out for this one. Ha.

I may be missing something deceptively simple, so if anyone can help me out here that'd be great!
 
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That Neuron said:
[itex]\Sigma[/itex]1 + (-1)n / n.
Do you mean this series:
$$\sum_{n=1}^{\infty}\left(1 + \frac{(-1)^n}{n}\right)$$
The first question to ask is whether the terms converge to zero. If not, the series cannot possibly converge.
 

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