$ a_k=\frac{1}{T}\int_0^Tx(t)e^{-jk\omega_0t}dt $.
And the equation for fourier series of a function is as follows:
$ x(t)=\sum_{k=-\infty}^{\infty}a_ke^{jk\omega_0t} $
We first put our signal into the first equation, and we get this monster:
$ a_0=\frac{1}{2\pi}\int_0^{2\pi}[4cos(2t) + (3j)sin(3t)]e^{0}dt $
