Does Absolute Convergence Follow from Convergence in Series?

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Homework Help Overview

The discussion revolves around the convergence of series, specifically addressing whether absolute convergence follows from convergence in the context of two series: one involving the terms \(X_n = \frac{1}{n^2}\) and another involving \(X^n\) divided by the factorial of \(n\).

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants explore the relationship between the convergence of a series and the convergence of its absolute values. Questions are raised about the importance of the value of \(X\) in the second series and the nature of convergence tests applicable to the series.

Discussion Status

Some participants have provided reasoning regarding the convergence of the first series, identifying it as a p-series and asserting its convergence. Others suggest using different tests, such as the ratio test, to analyze the second series, indicating a variety of approaches being considered without reaching a consensus.

Contextual Notes

There are indications of confusion regarding the definitions and implications of convergence and absolute convergence, as well as the need for clarity on the value of \(X\) in the second series. The discussion reflects an ongoing exploration of these concepts.

oswald
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Firs Question

If the serie


∑ Xn = (1/n²)
n=1

converge, then the serie |Xn| converge?

Second question

the serie

∑ X^n / [fat(n)] diverge?
n=1

where fat(n) = n(n-1)(n-2)...4.3.2.1

Its important know the value of X in X^n?
 
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oswald said:
Firs Question

If the serie


∑ Xn = (1/n²)
n=1

converge, then the serie |Xn| converge?

Second question

the serie

∑ X^n / [fat(n)] diverge?
n=1

where fat(n) = n(n-1)(n-2)...4.3.2.1

Its important know the value of X in X^n?

1)what is the || of 1/n^2?? think
2) search for geometric series and the hierarchy of infinities..

regards
marco
 
\sum_{n=0}^1 \frac{x^n}{n!}
is a well known Taylor's series for a simple function and your sum is only slightly different.
 
my answer
1)

∑ Xn = (1/n²) = 1 + 1/4 + 1/9 ... its a p-serie and converge because p=2>1.
n=1
and

∑ |Xn| = (1/n²) = 1 + 1/4 + ... its the same.. so its converge too.
n=1

2) converge using comparison test, no dought!
 
oswald said:
my answer
1)

∑ Xn = (1/n²) = 1 + 1/4 + 1/9 ... its a p-serie and converge because p=2>1.
n=1
and

∑ |Xn| = (1/n²) = 1 + 1/4 + ... its the same.. so its converge too.
n=1

2) converge using comparison test, no dought!

Better to use a ratio test. It will make it easy to see why the value of x doesn't matter.
 

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