## problem for differentiability of Fourier Series

In the lectures, lecturer just said,
f(x) needs to be continuous, 2L periodic, piecewise continuously differentiable on (-L,L)

is this the condition for differentiability of Fourier Series:

$B_{n}$ is the $\sin{\frac{n\pi x}{L}}$
term of f'(x),

then, $B_{n}=-\frac{n\pi a_{n}}{L}$