Ratio Test for Radius of Convergence | Solving sum(5^n)((x-3)^n)/n"

In summary, the Ratio Test for Radius of Convergence is a method used to determine the convergence or divergence of a series. It involves taking the limit of the absolute value of the nth term divided by the absolute value of the (n+1)th term as n approaches infinity. If the limit is less than 1, the series is absolutely convergent, if it is greater than 1 the series is divergent, and if it is equal to 1, another test must be used. This test can only be applied to series with positive terms and cannot be used to determine if a series is conditionally convergent. The radius of convergence can also be found by using the formula R = 1/lim<sub>n→
  • #1
thomas12323
2
0

Homework Statement



The problem is looking for the radius of convergence
sum(5^n)((x-3)^n)/n
n=1

Homework Equations





The Attempt at a Solution

 
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  • #2
What work have you done in using the ratio test?
 
  • #3
I broke it down to (x-3)n/(n+1)
 
  • #4
That's not right. What happened to the 5^n factor?
You should have this as part of your work.
[tex]\lim_{n \to \infty} \left(\frac{5^{n + 1}(x - 3)^{n + 1}}{n + 1}~\frac{n + 1}{5^n (x - 3)^n}\right )[/tex]
 

FAQ: Ratio Test for Radius of Convergence | Solving sum(5^n)((x-3)^n)/n"

1. What is the formula for the Ratio Test for Radius of Convergence?

The formula for the Ratio Test for Radius of Convergence is given by:
R = limn→∞ |an|/|an+1|, where an is the nth term of the series.

2. How do I apply the Ratio Test for Radius of Convergence to a series?

To apply the Ratio Test for Radius of Convergence, first find the nth term of the series. Then, take the absolute value of the nth term and divide it by the absolute value of the (n+1)th term. Finally, take the limit of this ratio as n approaches infinity. If the limit is less than 1, the series is absolutely convergent, and if the limit is greater than 1, the series is divergent. If the limit is equal to 1, the test is inconclusive and another test must be used.

3. Can the Ratio Test for Radius of Convergence be used on all series?

No, the Ratio Test for Radius of Convergence can only be used on series with positive terms. It cannot be used on alternating series or series with negative terms.

4. How do I use the Ratio Test for Radius of Convergence to find the radius of convergence?

To find the radius of convergence using the Ratio Test, first apply the test to the series. If the limit is less than 1, the radius of convergence is infinite. If the limit is greater than 1, the radius of convergence is 0. If the limit is equal to 1, the radius of convergence can be found by using the formula: R = 1/limn→∞ |an|^(1/n).

5. Can the Ratio Test for Radius of Convergence be used to determine if a series is conditionally convergent?

No, the Ratio Test for Radius of Convergence can only determine if a series is absolutely convergent or divergent. To determine if a series is conditionally convergent, the Alternating Series Test or the Ratio Test for Alternating Series must be used.

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