$ \begin{array}{ll}{\text { 1) }} & {X_{1}[\mathrm{n}]=\left[\frac{1}{3}\right]^{n} ; \mathrm{n} \geq 0} \ {\text { 2) }} & {X_{2}[\mathrm{n}]=X_{1}[\mathrm{n}+4]}\end{array} $