Construct the discrete Fourier coefficients for $f(x)= \begin{cases}-x, & 0 \leq x \leq \frac{1}{3} \pi \\ x-\frac{2}{3} \pi, & \frac{1}{3} \pi \leq x \leq \frac{4}{3} \pi \\ -x+2 \pi, & \frac{4}{3} \pi \leq x \leq 2 \pi\end{cases}$ based on $n=128$ sample points. Then graph the reconstructed function when using the data compression algorithm that retains only the 11 and 21 lowest-frequency modes. Discuss what you observe.