Taylor series radius of convergence and center

In summary, when approximating a function with a Taylor series, the series is centered around a given point a and converges within a certain radius R. This implies that there exists a Taylor series expansion centered at any point b within the interval [a-R, a+R]. However, we cannot determine if a series exists at the endpoints of the interval.
  • #1
azay
19
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When approximating a function with a Taylor series, I understand a series is centered around a given point a, and converges within a certain radius R. Say for a series with center a the interval of convergence is [a-R, a+R].

Does this imply that:

1. There also exists a Taylor series expansion centered in any of the other points in that interval?

2. If not, and one would like to describe the function in terms of Taylor series, in some interval [b-S, b+S] of a point b [tex]\in[/tex] [a-R, a+R] and b [tex]\neq[/tex] a. And let this interval [b-S, b+S] [tex]\subset[/tex] [a-R, a+R]. If there exists no Taylor series expansion centered in b, it is still possible to say something about the interval [b-S, b+S] by looking at the expansion centered in a. But how could one possibly know that a series then does exist in a? How do you find this a?
 
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  • #2
azay said:
1. There also exists a Taylor series expansion centered in any of the other points in that interval?

Yes, centered at any other point of the interval [tex](a-R,a+R)[/tex] . We don't know about the endpoints.
 

1. What is a Taylor series and why is it useful?

A Taylor series is a mathematical representation of a function as an infinite sum of terms. It is useful because it allows us to approximate functions that are difficult to evaluate directly by breaking them down into simpler terms.

2. What is the radius of convergence of a Taylor series?

The radius of convergence is a measure of how far away from the center of the series the function can still be accurately approximated. It is the distance from the center to the nearest point at which the series diverges.

3. How is the radius of convergence determined?

The radius of convergence is determined by the behavior of the function at the center of the series. It can be found using tests such as the Ratio Test or the Root Test, which examine the behavior of the terms in the series as the series approaches the center.

4. What happens if the radius of convergence is infinite?

If the radius of convergence is infinite, it means that the series converges for all values of the variable and the function can be approximated accurately at any point in its domain.

5. Can the radius of convergence be negative?

No, the radius of convergence is always a non-negative value. A negative radius of convergence would imply that the series converges outside of its domain, which is not possible.

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