For some reason, I haven't written it down, and the lecturer hasn't done it in his notes either, so it's probably in a lecture, which I could rewatch, but that means using up to 9hrs of my time trying to find that little bit about summation of Fourier series.
I got $-1+\sum_{m=0}^∞\frac{-12(-1)^{2m+1}+12}{(2m+1)^2π^2}cos(\frac{(2m+1)πx}{3})$
This should equal to $2x+2$ between $-3$ and (but not including) $0$, and $-2x+2$ between $0$ and (but not including) $3$.
I am asked to find the sum around $x=0$, except from understanding that x is 0, what do I do, is there any special way to calculate the sum of Fourier series?
The function is continous at $x=0$ (or the corresponding left and right limits are equal). Therefore the Fourier series converges to the value of the function at this point.