Question: The Fourier series expansion for the periodic function, $$ f(t) = |\sin(t)| $$ is defined in its fundamental interval. Taking $\pi = 3.142$, calculate the Fourier cosine series approximation of $f(t)$, up to the 6th harmonics when $t = 2.12$. Give your answer to 3 decimal places.
I have trouble understanding the meaning of fundamental interval. Does it mean that $[-\pi,\pi]$?
Usually the fundamental interval is the smallest period of the given function, so in this case $[0,\pi]$.