Converge absolutely or conditionally, or diverge?

  • Thread starter rcmango
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In summary, the conversation is about determining whether a given series converges absolutely, conditionally, or diverges. The individuals discuss using different convergence tests, such as the alternating series test and the nth term test for divergence, to determine the convergence of the series. Ultimately, it is determined that the series diverges by taking the limit of the summand as n goes to infinity.
  • #1
rcmango
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Homework Statement



heres the problem: http://img145.imageshack.us/img145/161/55180818ir8.png

does this series converge absolutely, conditionally, or does it diverge?

Homework Equations





The Attempt at a Solution



whats series to test it with?
at first glance it looks like an alternating series. reminds me of a failing p series in the denominator.
 
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  • #2
The very, very simplest of convergence tests: if a series converges the individual terms must go to 0. Does that happen here? What is
[tex]lim_{n\rightarrow \infty} \frac{(-1)^n}{10^{1/n}}[/tex]?
 
  • #3
Okay, it appears to be alternating, however it is not decreasing because of the denominator, it is increasing!

thus diverging by the alternating series test, correct?
 
  • #4
What he's using there is the nth term test for divergence. It should have been the first test that you learned, no?
 
  • #5
yes, an easy test, how do i take the nth term test to a variable with a n root? the 10^1/n is confusing me. please help.
 
  • #6
No, what I said was "If the individual terms do not go to 0, then the series must diverge"!

What is the limit of [tex]\frac{(-1)^n}{10^{(1/n)}}[/tex]? Is it 0?

If you have trouble with that, what about [itex]10^{1/n}[/itex] itself? Calculate a few values, say n= 10 and higher.
 
  • #7
i definitely can see that this does not go to 0.

However, how do I prove this on paper?

It fails convergence obviously.

Can i use direct comparison with harmonic series, and say that the harmonic series is smaller or equal to this series, thus showing if the harmonic series diverges, then the original series diverges.
 
  • #8
rcmango said:
However, how do I prove this on paper?

Just take the limit of the summand as n goes to infinity. You don't need to compare the series with anything.
 

FAQ: Converge absolutely or conditionally, or diverge?

What is the difference between absolute convergence and conditional convergence?

Absolute convergence means that a series converges regardless of the order in which its terms are arranged. Conditional convergence means that a series only converges if its terms are arranged in a specific order.

How can I determine if a series converges absolutely?

A series converges absolutely if the absolute value of its terms decreases as the series progresses and if the limit of these absolute values is less than 1. This is known as the ratio test.

Can a series converge conditionally but not absolutely?

Yes, it is possible for a series to converge conditionally but not absolutely. This occurs when the series satisfies the conditions for conditional convergence, but not absolute convergence.

What is the relationship between absolute convergence and conditional convergence?

All absolutely convergent series are also conditionally convergent, but the reverse is not necessarily true. In other words, if a series converges absolutely, it also converges conditionally, but a series that converges conditionally may or may not converge absolutely.

How do I know if a series diverges?

If the limit of the series' terms is not equal to 0, the series diverges. Additionally, if the series fails the convergence tests such as the ratio or root tests, it also diverges.

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