Exam Question 3 y[n] = x[n]*h[n]
$ = \sum_{k=-\infty}^\infty 2^ku[-k]u[-(n-k)] $
$ = \sum_{k=-\infty}^0 2^ku[-n+k] $
let r = -k
$ = \sum_{r=0}^\infty \frac{1^k}{2}u[-n-r] $
$ = \sum_{r=0}^{-n} \frac{1^k}{2} if -n \geqslant 0 $, 0 else
$ = \frac{1-0.5^{-n+1}}{1-0.5} if n \le 0 $ , 0 else
