The functions are-

$\displaystyle (a) f(x)=\left | x \right |, -\pi\leq x\leq \pi$

$\displaystyle (b) f(x)=\left | sin x \right |, -\pi\leq x\leq \pi$

Writing them individually

a)$\displaystyle f(x)=x $ and $\displaystyle f(x)=-x$

b)$\displaystyle f(x)=sin x$ and $\displaystyle f(x)=-sin x $

The problem is what should be the correct intervals for these functions. I am pretty messed up with this basic thing though I can easily compute the fourier series of these functions.