) Find the Fourier series for the function f(x)=\left\{\begin{array}{cc}

-1: & -\pi \leq x \leq 0 \\

1: & 0

\end{array}\right. defined on the interval [-, T]. (b) State the Intermediate Value Theorem and use it to show that f(x)=2 x^{4}-7 x^{2}+x+2 has four real solutions. (c) Let f(x)=\left\{\begin{aligned}

x &: x \leq 0 \\

-x &: x>0

\end{aligned}\right. Show that f(x) is not differentiable at x = 0. Explain your answer carefully.