Suppose that
f(x)=\begin{cases}1 − x, & 0\lt x \leq 1, \\0, & 1\lt x \leq 2.\end{cases} (13)
As indicated previously, we can represent f either by a cosine series or by a sine series. Sketch the graph of three periods of the sum of each of these series for −6 ≤ x ≤ 6.
In this example, L = 2, so the cosine series for f converges to the even periodic extension of f of period 4, whose graph is sketched in Figure 10.4.4.
Similarly, the sine series for f converges to the odd periodic extension of f of period 4. The graph of this function is shown in Figure 10.4.5.