course |
course_year |
question_number |
tags |
title |
year |
Methods |
IB |
50 |
|
Paper 1, Section II, A |
2011 |
Let $f(t)$ be a real function defined on an interval $(-T, T)$ with Fourier series
$$f(t)=\frac{a_{0}}{2}+\sum_{n=1}^{\infty}\left(a_{n} \cos \frac{n \pi t}{T}+b_{n} \sin \frac{n \pi t}{T}\right)$$
State and prove Parseval's theorem for $f(t)$ and its Fourier series. Write down the formulae for $a_{0}, a_{n}$ and $b_{n}$ in terms of $f(t), \cos \frac{n \pi t}{T}$ and $\sin \frac{n \pi t}{T}$.
Find the Fourier series of the square wave function defined on $(-\pi, \pi)$ by
$$g(t)=\left{\begin{array}{lr}
0 & -\pi<t \leqslant 0 \\
1 & 0<t<\pi
\end{array}\right.$$
Hence evaluate
$$\sum_{k=0}^{\infty} \frac{(-1)^{k}}{(2 k+1)}$$
Using some of the above results evaluate
$$\sum_{k=0}^{\infty} \frac{1}{(2 k+1)^{2}}$$
What is the sum of the Fourier series for $g(t)$ at $t=0$ ? Comment on your answer.