I'm getting started on Fourier series but I'm confused over the formulae involved.
My lecturers notes, including Wikipedia state that, for the interval $(-\pi \le x \le \pi)$
$$a_0 = \frac1\pi \int \cdots $$
whereas videos on Youtube and other tutorials I've found seem to be using:
$$a_0 = \frac1{2\pi} \int \cdots $$
Which one am I supposed to use?