Finding Fourier Series for f(x)=2x+e^x-e^-x (-1< x >1)

Click For Summary

Discussion Overview

The discussion revolves around finding the Fourier series for the function f(x) = 2x + e^x - e^-x over the interval (-1, 1). Participants are exploring methods of integration and properties of the function, including its classification as an odd function.

Discussion Character

  • Exploratory, Technical explanation, Mathematical reasoning, Homework-related

Main Points Raised

  • One participant requests assistance in finding the Fourier series for the given function and suggests it is an odd function.
  • Another participant corrects the interval notation from (-1 < x > 1) to (-1 < x < 1).
  • A participant suggests evaluating the integral of f(x)sin(πnx) from -1 to 1 as a method to find the Fourier coefficients.
  • One participant presents a transformation of the function, expressing it in terms of sinh(x) and discusses integration by parts, providing specific choices for u and dv.
  • Another participant recommends using integration by parts for the term xsin(ax) and suggests expressing sin(ax) in terms of exponential functions to simplify the integration process.

Areas of Agreement / Disagreement

Participants are generally in agreement about the approach to finding the Fourier series, but there are differing opinions on the specific methods for integration and the handling of terms within the function.

Contextual Notes

Participants have not fully resolved the integration steps or the implications of the function's properties on the Fourier series representation.

Who May Find This Useful

Students and enthusiasts interested in Fourier series, integration techniques, and the properties of odd functions in mathematical analysis.

bhajee
Messages
4
Reaction score
0
I wondered if someone could help me to find the Fourier series for this function please. I believe it's an odd function.

f(x) = 2x+e^x-e^-x (-1< x > 1)

This is my first post, so I'm going to try this LayTex typing too! Here goes!

[tex]f(x)=2x+e^x-e^-^x[/tex] (-1< x >1)

Thanks
 
Physics news on Phys.org
sorry!

(-1< x <1) Doh!
 
You need to evaluate the integral of f(x)sin(pi)nx from -1 to 1. Look it up in an integral table.
 
Here we are so far (can't get LaTex to work today!)

(e^x - e^-x)/2 = sinh(x)
so
2x + e^x - e^-x = 2x + 2sinh(x)

and for integration by parts
INT u.dv = uv - INT v.du
we have
u=2x+2sinh(x)

du=2+2cosh(x)

dv=sin(j*pi*x)

v=(1/j*pi)*cos(j*pi*x)

how am I going?
 
Try this: xsinax can be integrated by parts easily enough. For the other term, I would use sinax=(eiax-e-iax)/2i. Then all you have are the integrals of exponentials.
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 9 ·
Replies
9
Views
5K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 27 ·
Replies
27
Views
4K
  • · Replies 17 ·
Replies
17
Views
5K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 23 ·
Replies
23
Views
6K
  • · Replies 2 ·
Replies
2
Views
2K