Martinez's Fourier Assignment

Solve for a₃ for the waveform below:

T=6 seconds

<math>\begin{align} a_n &= \frac{2}{T}\int_0^T f(t)\cos(n\omega_0t)\, dt\\ b_n &= \frac{2}{T}\int_0^T f(t)\sin(n\omega_0t)\, dt\\ \because \!\T=6, dt\\ \end{align}