Problem $2.(0\mathrm{.}6$ points$)$ Consider the following discrete$-$time signals, please compute the Fourier

transform for each of the following signals.

$($a$)(0\mathrm{.}3$ points$)$ x$[$n$]=((1)/(3))^($n$-1)$u$[$n$]+3^($n$)$u$[-$n$+1].$

$($b$)(0\mathrm{.}3$ points$)$ x$[$n$]=[$cos$((\backslash$pi $)/(2)$n$+(\backslash$pi $)/(3))+2]*[$u$[$n$+1]-$u$[$n$-1]].$