Thread: Derivative of a fourier series

hello all...
I have this two 2_pi periodic function ..
Which of the following functions has a fourier series for iis derivative ??

(i) f(x) = x^3 [-pi<=x<pi]
(ii) f(x) = 0 ; -pi<=x<0
= 1-x ; 0<=x<pi

It will be helpful if you explain every step :-)

Thanks in advance

What's Fourier's theorem?