Abstract

Fourier series is an important mathematical concept. It is well known that we need too much computation to expand the function into Fourier series. The existing literature only pointed that its Fourier series is sine series when the function is an odd function and its Fourier series is cosine series when the function is an even function. And on this basis, in this paper, according to the function which satisfies different conditions, we give the different forms of Fourier series and the specific calculation formula of Fourier coefficients, so as to avoid unnecessary calculation. In addition, if a function is defined on [0,a], we can make it have some kind of nature by using the extension method as needed. So we can get the corresponding form of Fourier series.

Highlights

  • too much computation to expand the function into Fourier series

  • The existing literature only pointed that its Fourier series is sine series

  • we give the different forms of Fourier series

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Summary

Preliminary Knowledge

Definition 1 [1]-[3] Let f ( x) be an integrable function on [−l,l]. Are called the Fourier coefficients of f ( x). Definition 2 [1]-[5] Let f ( x) with the period 2l be an integrable function on [−l,l] , trigonometric series. Zhang with the Fourier coefficient are called Fourier series of f ( x) , denoted by f (x) a0 2. Lemma 1 [6] Let f ( x) be an integrable function on [−l,l] with period of 2l , the Fourier coefficients are ( ) calculated according to period of 2kl k ∈ N +. The calculation indicates there are same results between Fourier ( ) series with period of 2l and 2kl k ∈ N +

Calculating Fourier Series According to the Nature of the Function
Conclusion
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