Why are all of the even coefficients zero in the analysis on the previous
page?
Suppose you had a square wave that looked like the one below. Make
a Fourier series (of at least three terms) to approximate it. You'll soon
see that sines don't help. Why not?
Look at the square wave function written in summation notation on
the first page. Explain where the (2k
+ 1) terms come from.
In the Fourier series for the square wave, the coefficient decreased
(in this case, from 1 to 1/3 to 1/5) as we added more terms. That's typical
of Fourier series in general. Why do you think Fourier coefficients tend
to get smaller the further you get in the series?
Try building up
What shape will it have when you carry the series out to infinity?