$3\mathrm{.}6.$ Consider three continuous$-$time periodic signals whose Fourier series representations are as follows:

$x_1(t)={\displaystyle \underset{k=0}{\overset{100}{}}}(\frac{1}{2}{)}^k{e}^{jk\frac{2}{30}t}$

$x_2(t)={\displaystyle \underset{k=-100}{\overset{100}{}}}cos(k)e^{jk\frac{2}{50}t}$

$x_3(t)={\displaystyle \underset{k=-100}{\overset{100}{}}}$jsin$(\frac{k}{2})e^{jk\frac{2}{50}t}$