Find the First Four Terms (Rounded to Three Decimal Places)

Essay

Find the first four terms (rounded to three decimal places) of the Fourier series. Assume half-wave symmetry.
$\begin{array}{|c|c|c|c|c|c|c|c|}\hline\boldsymbol{x} & 0^{\circ} & 30^{\circ} & 60^{\circ} & 90^{\circ} & 120^{\circ} & 160^{\circ} & 180^{\circ} \\\hline\boldsymbol{y} & 0 & 3.1 & 4.5 & 8.1 & 15.1 & 14.4 & 0 \\\hline\end{array}$