Ratio Test inconclusive with factorial

In summary, the Ratio Test is a mathematical tool used to determine whether an infinite series converges or diverges. It involves comparing the ratio of consecutive terms to a known value and can be used with factorials by taking the limit as n approaches infinity. When the Ratio Test is inconclusive, it means that other tests may be needed to determine the convergence or divergence of a series. Additionally, the Ratio Test is not always reliable and should be used in conjunction with other methods and tests.
  • #1
micast87
1
0

Homework Statement



[tex]\sum(n-1)!/(n+2)![/tex]

2. The attempt at a solution

I tried the ratio test and came up with the lim[tex]_{}n\rightarrow\infty[/tex] n/(n+3) = 1 which gives no information on convergence or divergence. I'm trying to find absolute or conditional convergence so what else can I do?
 
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  • #2
You can first simplify that sum into 1/[(n+2)(n+1)(n)] = 1/[n^3 +3n^2 + 2n].

Then do comparison test using another sum: 1/n^3,

Since the latter is greater than the former and it converges, therefore the original series converges. For absolute convergence, just remember to take the absolute value of the original series.
 

Related to Ratio Test inconclusive with factorial

1. What is the Ratio Test?

The Ratio Test is a mathematical test used to determine whether an infinite series converges or diverges. It involves comparing the ratio of consecutive terms in the series to a known value, such as 1 or 0.

2. How is the Ratio Test used with factorials?

In the context of factorials, the Ratio Test is used to determine the convergence or divergence of a series involving factorials. The test involves taking the limit of the ratio of consecutive terms in the series as n approaches infinity.

3. What does it mean when the Ratio Test is inconclusive?

When the Ratio Test is inconclusive, it means that the test did not provide enough information to determine whether the series converges or diverges. This could be due to the ratio of consecutive terms being equal to 1, or approaching 1 as n approaches infinity.

4. Are there other tests that can be used to determine convergence or divergence when the Ratio Test is inconclusive?

Yes, there are other tests that can be used in conjunction with the Ratio Test to determine the convergence or divergence of a series. For example, the Integral Test or the Comparison Test can also be used to evaluate the convergence or divergence of a series.

5. Is the Ratio Test always reliable in determining convergence or divergence?

No, the Ratio Test is not always reliable in determining convergence or divergence. It can provide inconclusive results in certain cases, and there are also series for which the Ratio Test may indicate convergence, but the series actually diverges. Therefore, it is important to use other tests and methods in addition to the Ratio Test to fully evaluate the convergence or divergence of a series.

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