Answer
$a_n = (-1)^n = \{-1,1,-1,1,...\}$
Work Step by Step
$a_n = (-1)^n$ is bounded by the values $-1$ and $1$, since the terms are either $-1$ or $1$. The limit doesn't exist because the terms do not approach one value. They simply alternate between the values $-1$ and $1$.
