- #1
BOAS
- 552
- 19
1. Homework Statement
Find the Fourier series of
##f(x) = \delta (x) - \delta (x - \frac{1}{2})## , ## - \frac{1}{4} < x < \frac{3}{4}##
periodic outside.
Homework Equations
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##\int dx \delta (x) f(x) = f(0)##
##\int dx \delta (x - x_0) f(x) = f(x_0)##
The Attempt at a Solution
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I am struggling to visualise this function, which is making it hard to tell if my series makes sense. Plus I find the delta function a little confusing to reason about.
The function has a period of 1.
##a_0 = 2 \int^{3/4}_{-1/4} \delta (x) dx - 2 \int^{3/4}_{-1/4} \delta (x - \frac{1}{2}) dx = 0##
##a_n = 2 \int^{3/4}_{-1/4} \delta (x) \cos (n \pi x) dx - 2 \int^{3/4}_{-1/4} \delta (x - \frac{1}{2}) \cos (n \pi x)dx = 2 - 2 \cos (\frac{n \pi}{2})##
##b_n = 2 \int^{3/4}_{-1/4} \delta (x) \sin (n \pi x) dx - 2 \int^{3/4}_{-1/4} \delta (x - \frac{1}{2}) \sin (n \pi x) dx = -2 \sin (\frac{n \pi}{2})##
I think those are my Fourier coefficients, and I couldn't find a nice way to express them, so I think they're ok left as trig functions.
Does it look ok?