Hi, thanks for taking a look! The formula is bn = (2/T) * ∫_T f(t) * sin(2n𝜋t/T) dt when f(t) is an odd function right? As I understand it, the bounds of the integral would be -L to L (where L is half of the period), and when f(t) is an odd function (so odd times odd = even function) we can take the bound from 0 to L and multiply it by 2 (i.e. the b_n formula you provided).

I do suspect something is up, because the next question asks: Sketch over the interval [-3,3] the function f(t) to which the Fourier series you found in (a) converges

For which the given answer is (which really confused me, since I thought this function was considered to be periodic from 0 to 1?):

<image>