Comparing Series Convergence: Limit or Direct Comparison Test?

In summary, a comparison test for series is a method used to determine the convergence or divergence of a series by comparing it to a known series with known convergence properties. It works by comparing the given series to a known series that has already been proven to converge or diverge. The main types of comparison tests are the limit comparison test, the ratio test, and the integral test. A comparison test is most useful when the given series is difficult to evaluate directly, but it can be compared to a known series with known convergence properties. However, it can only be used if there is a known series to compare to and may not work if the given series is significantly different from the known series being compared to.
  • #1
waealu
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Homework Statement


Does the following series converge or diverge (use either the Limit Comparison or the Direct Comparison Test):

[tex]\sum_{n=1}^{+\infty} \frac{3^{n-1}+1}{3^{n}}[/tex]


Homework Equations



In a previous problem that was
[tex]\sum_{n=1}^{+\infty} \frac{1}{3^{n-1}+1}[/tex]
I was able to reindex the series to make it
[tex]\sum_{n=0}^{+\infty} \frac{1}{3^{n}+1}[/tex]
From there, I took 1/(3n+1)<1/3n.

Therefore, since 1/3n converges, [tex]\sum_{n=1}^{+\infty} a_{n}[/tex] also converges.


The Attempt at a Solution



However, I don't know how to solve the series that I'm currently on.

Thanks,
Erik
 
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  • #2
(3^(n-1)+1)/3^n>1/3, isn't it?
 

1. What is a comparison test for series?

A comparison test for series is a method used to determine the convergence or divergence of a series by comparing it to a known series with known convergence properties.

2. How does a comparison test work?

A comparison test works by comparing the given series to a known series that has already been proven to converge or diverge. If the given series is "less than" or "equal to" the known series, and the known series converges, then the given series also converges. If the given series is "greater than" or "equal to" the known series, and the known series diverges, then the given series also diverges.

3. What are the different types of comparison tests?

The main types of comparison tests are the limit comparison test, the ratio test, and the integral test. Other variations of these tests, such as the direct comparison test and the alternating series test, also exist.

4. When should I use a comparison test?

A comparison test is most useful when the given series is difficult to evaluate directly, but it can be compared to a known series with known convergence properties. It is also useful when the given series contains terms that are similar to those of a known series.

5. What are the limitations of a comparison test?

A comparison test can only determine the convergence or divergence of a series if it can be compared to a known series. If there is no known series to compare to, then the comparison test cannot be used. Additionally, the comparison test may not work if the given series is significantly different from the known series being compared to.

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