What is the Fundamental Frequency in the Fourier Series of cos4t + sin8t?

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Discussion Overview

The discussion revolves around determining the fundamental frequency in the Fourier series representation of the function x(t) = cos4t + sin8t. Participants explore the implications of combining functions with different frequencies and the choice of the fundamental frequency ω0.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about the appropriate value of ω0 given the combination of cos4t and sin8t.
  • Another participant presents the standard form of a Fourier series, indicating that the coefficients A_8 and B_4 are non-zero while others are zero.
  • A different participant suggests that the series can be expressed as An*cos(nω0t) + Bn*sin(nω0t), indicating a preference for this representation.
  • It is noted that while the standard presentation of Fourier series does not require ω0, choosing a specific ω0 can simplify expressions, with a suggestion to use ω0=1 for this case.

Areas of Agreement / Disagreement

Participants have differing views on the necessity and implications of choosing a specific ω0. There is no consensus on the best approach to represent the Fourier series in this context.

Contextual Notes

The discussion highlights the dependence on the choice of ω0 and its effect on periodicity, but does not resolve how this choice impacts the overall representation of the Fourier series.

helderdias
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Hi everyone,

So I was trying to calcule the Fourier Series of x(t) = cos4t + sin8t, but I'm a little bit confused. What would be ω0 in this case since I have a combination of two functions with different frequencies?

Thank you in advance.
 
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I don't know what you mean by [itex]\omega_0[/itex] here. A Fourier series is a sum
[tex]\sum_{n=0}^\infty A_n sin(nt)+ B_n cos(nt)[/tex]
Here, obviously [itex]A_8= 1[/itex], [itex]B_4= 1[/itex] and all other coefficients are 0.
 
I thought the series was the sum of An*cos(nw0t) + Bn*sen(nw0t)
 
Typically Fourier series are presented as HallsofIvy posted. However, there's no reason not to include a frequency term [itex]\omega_0[/itex]. This can simplify some expressions, and you are free to choose any [itex]\omega_0[/itex] you like. It's important to remember that any choice of [itex]\omega_0[/itex] changes the periodicity to [itex]\frac{2\pi}{\omega_0}[/itex].

For your example, it's clearly best to choose [itex]\omega_0=1[/itex]
 

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