Finding Fourier Series of sin(a*pi*t): Results & Confirmation

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SUMMARY

The discussion focuses on finding the Fourier series for the function sin(a*pi*t) and the implications of the parameter 'a' approaching 1/L. Participants highlight common pitfalls, such as incorrectly assuming that certain sine terms yield zero, particularly when 'a' is not an integer. The formula for calculating the coefficients b_n is emphasized, specifically noting that b_n will be zero if n equals a, leading to confusion among students. The importance of correctly defining the interval and the assumptions made during calculations is also underscored.

PREREQUISITES
  • Understanding of Fourier series and their coefficients, specifically b_n.
  • Familiarity with the properties of sine functions and their behavior over defined intervals.
  • Knowledge of calculus, particularly integration techniques used in Fourier analysis.
  • Concept of integer versus non-integer values in mathematical functions.
NEXT STEPS
  • Study the derivation of Fourier series coefficients, focusing on the formula b_n = (1/π) ∫_{-π}^π sin(3x)sin(nx) dx.
  • Explore the implications of varying 'a' in the function sin(a*pi*t) and its effect on the Fourier series expansion.
  • Learn about the convergence properties of Fourier series, especially in relation to non-integer values of 'a'.
  • Investigate common errors in Fourier series calculations and how to avoid them in practical applications.
USEFUL FOR

Students studying Fourier analysis, mathematics educators, and anyone involved in signal processing or harmonic analysis who seeks to deepen their understanding of Fourier series and their applications.

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Homework Statement



Find the Fourier series for: sin(a*pi*t). Consider what happens when a -> 1/L

Homework Equations





The Attempt at a Solution



I keep getting zeros for a_o, a_n, and b_n.

I though that atleast b_n should give me something, can anyone also confirm this?
 
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What is L? Are you trying to find an expansion on (-L,L) using terms like \sin{(n\pi x/l)} And are you assuming in your calculations that a is an integer? If a is not an integer you should get lots of bn terms. Make sure you haven't assumed that terms like \sin{a\pi} are zero in your calculations. Hard to guess without seeing your work.
 
Sorry for wasting your time, but I didn't feel like typing up a page of work.
 
It might not be wasting either of our times. A common mistake students make when, for example, trying to find the Fourier series for sin(3x) on (-\pi,\pi) is to think the formula for

b_n=\frac 1 \pi \int_{-\pi}^\pi \sin{(3x)}\sin{(nx)}\ dx

works when n = 3, which it doesn't. So they are puzzled why all the bn are zero. Your question made me think you might be making one or both that type of error or assuming a is an integer.
 

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