Find the exponential Fourier transform of the given $f(x)$ and write $f(x)$ as a Fourier integral [that is, find $g(\alpha)$ in equation (12.2) and substitute your result into the first integral in equation $(12.2)]$
$$f(x)=\left\{\begin{array}{rr}
-1, & -\pi < x < 0 \\
1, & 0 < x < \pi \\
0, & |x| > \pi
\end{array}\right.$$