Fourier series and calculate integral

Power-reduction_formulasIn summary, the conversation is about expanding a function in Fourier series and calculating its integral. The function is f(x)= (sinx)^2(cosx)^3 with a period of 2π. The suggested approach is to express cos3(x) as (1 - sin2(x))cos(x) and use the substitution u = sin(x). The function is even, so its Fourier expansion will have only cosine terms. The power-reduction formulas for trigonometric identities can be used to rewrite the function in terms of its Fourier series.
  • #1
rayman123
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Homework Statement


expand the function in Fourier series and calculate the integral
[tex] f(x)= (sinx)^2(cosx)^3, 2\pi [/tex] is the period
calculate the integral
[tex] \int_{0}^{2\pi}f(x)dx[/tex]
please help...have absolutely no idea how to calculate it...


Homework Equations





The Attempt at a Solution




 
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  • #2
Express the cos3(x) as (1 - sin2(x))cos(x) and use the substitution u = sin(x).
 
  • #3
rayman123 said:

Homework Statement


expand the function in Fourier series and calculate the integral
[tex] f(x)= (sinx)^2(cosx)^3, 2\pi [/tex] is the period
calculate the integral
[tex] \int_{0}^{2\pi}f(x)dx[/tex]
please help...have absolutely no idea how to calculate it...
Note that f(x) is even, so what does this tell you about its Fourier expansion?

You can use trig identities to rewrite f(x) as a Fourier series, instead of having to crank out the integrals. In particular, look at the power-reduction formulas, and use what you know about what its Fourier expansion should look like to guide you.

http://en.wikipedia.org/wiki/List_of_trigonometric_identities
 

1. What is a Fourier series?

A Fourier series is a mathematical representation of a periodic function as a sum of sine and cosine waves with different frequencies and amplitudes. It is used in many areas of science and engineering to analyze and model periodic phenomena.

2. How do you calculate a Fourier series?

To calculate a Fourier series, you need to find the coefficients of the sine and cosine terms using the integral formula. These coefficients can then be used to construct the Fourier series, which is an infinite sum of sine and cosine terms.

3. What is the purpose of calculating integrals in Fourier series?

Calculating integrals is crucial in finding the coefficients of the sine and cosine terms in a Fourier series. Without these coefficients, the Fourier series cannot be accurately represented and used to analyze the original function.

4. Can Fourier series be used for non-periodic functions?

No, Fourier series can only be used to represent periodic functions. However, there are other methods, such as the Fourier transform, that can be used to analyze and represent non-periodic functions.

5. Are there any real-world applications of Fourier series?

Yes, Fourier series are used in many fields, including signal processing, image and sound compression, and analyzing electrical circuits. They are also used in solving differential equations and studying heat transfer and fluid dynamics.

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