Find the Fourier transform of the function $f(t)=\exp (-|t|)$
(a) By applying Fourier's inversion theorem prove that
$$
\frac{\pi}{2} \exp (-|t|)=\int_{0}^{\infty} \frac{\cos \omega t}{1+\omega^{2}} d \omega
$$
(b) By making the substitution $\omega=\tan \theta$, demonstrate the validity of Parseval's theorem for this function.