How Do You Simplify and Find the Interval of Convergence for a Power Series?

In summary, the interval of convergence for the given series is abs(x)/3. The ratio test was used to simplify the expression and the limit was taken as n approaches infinity, resulting in the final interval of convergence.
  • #1
tolove
164
1
Edit: Nevermind, figured it out. Thank you for readingOriginal problem:
Find the interval of convergence
[itex]\sum[/itex]n=1 xn / n * √(n) * 3n

Ratio Test, right? an+1/a

I get to here and I can't figure out how to get rid of the ns:

lim n→∞ abs(x/3)* [n*√(n) / (n+1)*√(n+1)]

Solution,
They break apart evenly:
(n/(n+1)) * (n/(n+1)**(1/2)

(also, sorry this looks terrible. I'm not sure how to use the graphics options very well yet)
 
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  • #2
tolove said:
Original problem:
Find the interval of convergence
[itex]\sum[/itex]n=1 xn / n * √(n) * 3n

Ratio Test, right? an+1/a

I get to here and I can't figure out how to get rid of the ns:

lim n→∞ abs(x/3)* [n*√(n) / (n+1)*√(n+1)]

(also, sorry this looks terrible. I'm not sure how to use the graphics options very well yet)

Start with just the n/(n+1) part. Divide numerator and denominator by n and tell me what the limit of that is as n->infinity.
 
  • #3
Dick said:
Start with just the n/(n+1) part. Divide numerator and denominator by n and tell me what the limit of that is as n->infinity.

Simplifies down to:
limn→∞ abs(x)/3 * (1/(1+1/n))**(3/2) = abs(x)/3

Thank you very much for your reply!
 

Related to How Do You Simplify and Find the Interval of Convergence for a Power Series?

1. What is a power series?

A power series is an infinite sum of terms in the form of a constant multiplied by a variable raised to a non-negative integer power. It is a type of mathematical function that can be used to represent a wide range of functions in calculus and analysis.

2. How do you simplify a power series?

To simplify a power series, you can use various techniques such as factoring, partial fraction decomposition, and substitution. It is also important to understand the properties of power series, such as the rules for manipulating exponents and coefficients, in order to simplify them effectively.

3. Why is simplifying power series useful?

Simplifying power series can help make complex functions more manageable and easier to work with. It can also provide insights into the behavior of a function and help in finding patterns or relationships between different functions.

4. What are some common applications of power series?

Power series are used in a variety of fields, including physics, engineering, finance, and statistics. They are particularly useful in solving differential equations, approximating functions, and analyzing the behavior of systems and processes.

5. What is the difference between a Taylor series and a Maclaurin series?

A Taylor series is a type of power series that is used to represent a function at a specific point, while a Maclaurin series is a special case of a Taylor series where the point used is 0. In other words, a Maclaurin series is a Taylor series centered at 0.

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