Root test vs. ratio test question

In summary, the conversation involves a practice problem for an exam, specifically a sum from n=0 to infinity. The book suggests using the ratio test on the problem, but the question arises if the root test could also be applied. The root test is determined to be the simpler option and the individual shares their conclusion based on their initial attempt at using the ratio test.
  • #1
cue928
130
0
I am doing the following practice problem in prep for an exam:
sum from n=0 to infinity: (3^n)/(n+1)^n
The book says to use the ratio test on it, which I did, but would the root test also apply to this?
 
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  • #2
The root test applies, and in fact is probably the simplest test to use in this case. What was your conclusion based on the ratio test?
 
  • #3
cue928 said:
I am doing the following practice problem in prep for an exam:
sum from n=0 to infinity: (3^n)/(n+1)^n
The book says to use the ratio test on it, which I did, but would the root test also apply to this?


Well...

[tex]\sqrt[n]{\frac{3^n}{(n+1)^n}} =[/tex]

.
.
.
 
  • #4
I had initially changed it to be:
(3/(1+n))^n. Applying the nth square root, I got lim n approaches infinity 3/1+n = 0.
 
  • #5
cue928 said:
I got lim n approaches infinity 3/1+n = 0.

Ok, so what's the conclusion?
 

1. What is the difference between the root test and the ratio test?

The root test and the ratio test are both used to determine the convergence or divergence of infinite series. The main difference between them is the way they evaluate the terms of the series. The root test involves taking the nth root of the absolute value of each term, while the ratio test involves taking the limit of the absolute value of the ratio between consecutive terms.

2. Which test should I use to determine convergence?

The answer to this question depends on the specific series you are dealing with. In general, the root test is more powerful and can be used for a wider range of series. However, there are some cases where the ratio test may be more suitable. It is always a good idea to try both tests and see which one gives a conclusive result.

3. Are there any limitations or assumptions for using these tests?

Yes, both the root test and the ratio test have some limitations and assumptions. For the root test, the series must have positive terms and the limit of the nth root of the terms must exist. For the ratio test, the series must have positive terms and the limit of the ratio between consecutive terms must exist.

4. What is the significance of the convergence or divergence of a series?

The convergence or divergence of a series indicates whether the sum of all the terms of the series approaches a finite value or not. If the series converges, it means that the sum of all the terms is finite, and if it diverges, it means that the sum of all the terms is infinite.

5. Can the root test and ratio test be used for any type of series?

No, these tests are specifically designed for infinite series. They cannot be used for finite series or series with a finite number of terms. Additionally, they are most commonly used for series with positive terms, although there are some modifications that can be made for series with negative terms.

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