Does the Alternating Series Converge Conditionally?

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In summary, the conversation is about finding an equation that converges conditionally using the alternating series equation. The equation in the picture is meant to be read as \sum_{n=2}^{\infty}\frac{(-1)^nn}{1+nlNn}. The solution involves checking the two conditions for an alternating series to converge, namely the last term converging to zero and the terms being non-increasing. Using L'Hopital's rule can help determine if the derivative is negative for positive infinity, which would indicate convergence.
  • #1
rcmango
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Homework Statement



heres the equation that will converge conditionally: http://img440.imageshack.us/img440/9945/untitled3jg.jpg

changes to
An = n/(1 + nLNn)

Homework Equations


alternating series equation.
converges conditionally.

d/dn An = (1-n)/(1+nLNn)^2

The Attempt at a Solution



I'm not sure how the first equation changes to the second equation, and then I'm supposed to use l'hopitals rule.

any help please.
 
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  • #2
Is the equation in the picture meant to read [tex]\sum_{n=2}^{\infty}\frac{(-1)^nn}{1+nlNn}[/tex]?

Try to learn LaTex; it's very easy to use. Click on the equation to see the code. The tutorial is here: https://www.physicsforums.com/showthread.php?t=8997
 
  • #3
An alternating series converges if it meets two conditions: The last term converges to zero and the terms, ignoring the signs, are non-increasing.

The 1st one is met easily. for the 2nd check check the derivative, if its negative for positive infinity, then it converges.
 

1. What does it mean for a series to converge absolutely?

Converging absolutely refers to the convergence of a series in which the absolute value of each term decreases and approaches zero. It is a stronger form of convergence than conditional convergence, in which the series may still converge even if the absolute values of the terms do not approach zero.

2. How is absolute convergence different from conditional convergence?

Absolute convergence requires that the absolute values of the terms in a series decrease and approach zero, whereas conditional convergence only requires that the terms themselves decrease and approach zero. This means that a series that converges absolutely will also converge conditionally, but the reverse is not necessarily true.

3. What is the significance of absolute convergence?

Absolute convergence is important because it guarantees the convergence of a series, regardless of the order in which the terms are added. This allows for more flexibility in manipulating and rearranging series, making it easier to solve problems in mathematics and other fields that rely on series.

4. How can I determine if a series converges absolutely?

To determine if a series converges absolutely, you can use the ratio test or the comparison test. The ratio test compares the series to a geometric series, while the comparison test compares it to a known convergent or divergent series. If the limit of the ratio test is less than 1 or the series being compared to is convergent, then the series in question converges absolutely.

5. What are some real-world applications of absolute convergence?

Absolute convergence has many practical applications, such as in the fields of physics and engineering. For example, in electrical engineering, absolute convergence is used to analyze alternating current circuits. In physics, it is used in the study of quantum mechanics and in predicting the behavior of particles. It is also used in economics and finance to analyze time series data and make predictions about market trends.

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