The function y(t) in this example is the periodic continuous-time signal cos(x) such that
$ y(t) = \ cos(x) $
where cos(x) can be expressed by the Maclaurin series expansion
$ \ cos(x) = \sum_{n=0}^\infty a_n x^n $
where its Fourier series coefficients are described by the equation
$ \left ( \frac{1}{jk\omega_0} \right )a_k = \left ( \frac{1}{jk \left (2\pi/T \right)} \right )a_k $
