Convergence of series using ratio test

In summary, the conversation discusses proving the convergence of a series using the ratio test, but the test is not applicable in this case due to the limit of the series being equal to 1. The conversation ends with a question about alternative convergence tests.
  • #1
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Homework Statement


assume summation of series An converges with all An>0. Prove summation of sqrt(An)/n converges

Homework Equations





The Attempt at a Solution


I Tried using the ratio test which says if lim as n goes to infinity of |Bn+1/Bn|<1 then summation of Bn converges. I let Bn be Sqrt(An)/n and we have...

lim as n goes to infinity of |(sqrt(An+1/An)*n/n+1|. limit of n/n+1 goes to one so i need to prove that |sqrt(An+1/An)|<1. But I got stuck because just because An converges does not mean that |(An+1/An)|<1. Can someone help me or suggest on a different convergence test that I should use?
 
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  • #2
For your series,
[tex]\lim_{n \to \infty} \sqrt{\frac{a_{n+1}}{a_n}} = 1[/tex]

so the Ratio Test is not going to be any help.

What other tests do you know?
 

FAQ: Convergence of series using ratio test

What is the ratio test?

The ratio test is a method used to determine the convergence or divergence of a series. It involves taking the limit of the ratio of successive terms in the series and using this limit to determine the behavior of the series.

When should the ratio test be used?

The ratio test should be used when the terms in the series involve exponentials, factorials, or other expressions that can be simplified using the ratio of successive terms. It is also useful when the terms in the series do not have a clear pattern or do not fit into other convergence tests.

What does the ratio test tell us about the convergence of a series?

The ratio test tells us whether a series is absolutely convergent, conditionally convergent, or divergent. If the limit of the ratio of successive terms is less than 1, the series is absolutely convergent. If the limit is greater than 1, the series is divergent. If the limit is equal to 1, further tests are needed to determine the convergence.

Can the ratio test be used for all series?

No, the ratio test can only be used for series with positive terms. Additionally, if the limit of the ratio of successive terms is equal to 1, further tests may be needed to determine the convergence or divergence of the series.

How do we use the ratio test to determine the convergence of a series?

To use the ratio test, we first take the limit of the ratio of successive terms. If the limit is less than 1, the series is absolutely convergent. If the limit is greater than 1, the series is divergent. If the limit is equal to 1, further tests may be needed to determine the convergence or divergence of the series.

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