How to find the period of a Fourier Series

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Discussion Overview

The discussion revolves around determining the period of a Fourier series, specifically in the context of the function f(t) = t defined on the interval [-π, π]. Participants express confusion regarding the period, with some suggesting it is π while others argue for a period of 2π.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant states that they believe the period of f(t) = t is 2π, based on their understanding of the function's definition over the interval [-π, π].
  • Another participant suggests that if all odd coefficients are zero, then the function is even, leading to the conclusion that it is periodic with period π.
  • A different viewpoint argues against the idea that the function can have a period of π, stating that the function from -π to 0 is a mirror image of the function from 0 to π, which implies a different periodicity.
  • One participant emphasizes that the problem statement must provide sufficient information to determine the period, noting that if the Fourier series is meant to represent the function on (-π, π), then the period must be at least 2π.
  • They also provide an example of a function g(t) = t on (-2π, 2π) and suggest that a 4π periodic Fourier series could represent it, which would differ from the original function on the specified interval.

Areas of Agreement / Disagreement

Participants express differing views on the correct period of the function, with no consensus reached. Some argue for a period of π while others maintain that it should be 2π, indicating an unresolved debate on the topic.

Contextual Notes

The discussion highlights the importance of clearly defining the function's domain and the intended periodicity when working with Fourier series, as assumptions about these factors can lead to different conclusions.

thecaptain90
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Hi. My problem is that even though I can find the Fourier series, its coefficients etc. I have trouble determining the period of equation. For example let's say we have f(t) = t, t \in [-pi,pi]. I thought that the period was 2pi but in the solution it says that the period is pi. This isn't the first time that I couldn't determine the period of an equation in order to find the Fourier series. Can someone make things clear for me?
Thanks.
 
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Are all the odd coefficients 0? If that is true, then the function is an even function, f(-x)= f(x), so that its values from -\pi to 0 are identical to its values from 0 to \pi. That, together with the obvioius "periodic with period 2\pi" means it is periodic with period \pi.
 
HallsofIvy said:
Are all the odd coefficients 0? If that is true, then the function is an even function, f(-x)= f(x), so that its values from -\pi to 0 are identical to its values from 0 to \pi. That, together with the obvioius "periodic with period 2\pi" means it is periodic with period \pi.
<br /> <br /> Not so: The function from -π to 0 is the mirror image of the function from 0 to π. In order to have a period of π, it needs to be a translate in this domain.
 
thecaptain90 said:
Hi. My problem is that even though I can find the Fourier series, its coefficients etc. I have trouble determining the period of equation. For example let's say we have f(t) = t, t \in [-pi,pi]. I thought that the period was 2pi but in the solution it says that the period is pi. This isn't the first time that I couldn't determine the period of an equation in order to find the Fourier series. Can someone make things clear for me?
Thanks.

The statement of the problem needs to give you enough information to determine the period. In your example, if the FS it to represent the function on (-pi,pi), its period must be at least 2pi. But unless you state that the given formula represents one period, you can't say for sure what FS you are talking about. For example, if you take g(t) = t on (-2pi,2pi) and write a 4pi periodic FS for it, it will equal your f(t) on (-pi,pi).
 

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