Fourier Series Problem.

I have this question on my assignment:
Write the Fourier series for the 2-periodic function defined
as f(x) = |x| on [-1, 1] and then by choosing the correct value of x,
find the sum form j = 0 to infinity [1/(2j+1)^2].
Plot your result on the same axes as the
function to compare.

I got got the Fourier Series and have plotted them and compared them ez. But I'm not sure what the part about find the correct value of x to solve the sum is talking about. Please help.

Without doing the work I'm guessing that with the right choice of x value you will get

|x| = constant + constant * (your sum)

I haven no idea what you are talking about :S

I know what the Fourier Series is if that helps at all, it's:
f(x) = (1/2)+sum k=1 to infinity 2[((-1)^k-1)/(pi^2*k^2))*cos(k*pi*x)]

halp? :(

Strange, I make it and with x=1 it certainly gives the correct answer for the sum.