(Question 3)
Let $f(x)$ be a function of period $2\pi$ such that, $f(x) = \begin{cases} x, & 0 < x < \pi \\ \pi, & \pi < x < 2\pi \end{cases}$
(a) Sketch a graph of $f(x)$ in the interval $-2\pi < x < 2\pi$. (5 marks)
(b) Determine that the Fourier series for $f(x)$ in the interval of $-2\pi < x < 2\pi$. (20 marks)