Convergence of a Series with Exponential Terms

  • Thread starter Mattofix
  • Start date
  • Tags
    Series
In summary, the conversation is about determining whether a given series converges or diverges. One person suggests using the ratio test and another suggests using a comparison test. The expert recommends using the comparison test, stating that the nth term in the series is (1+e^(-n))/((n+1)^2-(n-1)^2) and that it is larger than 1/4n, which diverges. Therefore, the series also diverges.
Physics news on Phys.org
  • #2
i feel like I am going in the totally wrong direction - if so please can someone please point me the right way.
 
  • #3
Expand the denominator first. The n^2 terms cancel so the denominator is basically proportional to n. The numerator, I think, tends to 1. Do you agree? So do you think it converges or diverges? It's good to have opinion to organize the strategy before you start trying to prove anything.
 
  • #4
I am getting:

1+exp(-n)
----------
4n.e^n

Now, using ratio test I can prove that 1/(4n.e^n) is converging, and I also know that 1+exp(-n) is converging so that means there product is converging?

My Second approach

lim n--> inf (this series)/ [(1+exp(n))/exp(n)] is equal to 0, so this is equivalent to:
exp(n)+1
----------
exp(n)

now this seems wrong because my series does not converge. What have done wrong here?
 
  • #5
The nth term in the series is (1+e^(-n))/((n+1)^2-(n-1)^2). The denominator is 4n. The numerator converges to one. It's begging for a comparison test.
 
  • #6
thanks.

(1+exp(-n))/4n > 1/4n

and since 1/4n diverges so must the series.
 

FAQ: Convergence of a Series with Exponential Terms

What does it mean for a series to converge?

When a series converges, it means that the infinite sum of its terms approaches a finite number as the number of terms increases. In other words, the sum of the terms in the series gets closer and closer to a specific value as more terms are added.

How can you tell if a series converges or diverges?

There are several tests that can be used to determine if a series converges or diverges, such as the ratio test, the comparison test, and the integral test. These tests compare the given series to a known convergent or divergent series to determine its behavior.

What is the difference between absolute convergence and conditional convergence?

Absolute convergence refers to a series where the sum of the absolute values of its terms is convergent. Conditional convergence refers to a series where the sum of its terms is convergent, but the sum of the absolute values of its terms is divergent. In other words, in conditional convergence, the series only converges when certain terms are added in a specific order.

Can a series converge and diverge at the same time?

No, a series can either converge or diverge, but not both at the same time. If a series diverges, it means that the sum of its terms approaches infinity as the number of terms increases. If a series converges, it means that the sum of its terms approaches a finite number as the number of terms increases.

How can you use the limit comparison test to determine if a series converges?

The limit comparison test compares the given series to a known series and takes the limit of the ratio of their terms. If the limit is a finite positive number, then the given series converges if and only if the known series also converges. If the limit is zero or infinite, the test is inconclusive and another test must be used to determine the convergence of the given series.

Back
Top