Calculus: Early Transcendentals (2nd Edition)

$a_n = \frac{1}{n} = \{1,\frac{1}{2},\frac{1}{3},\frac{1}{4},...\}$
$a_n = \frac{1}{n}$ is bounded by $0$ and $1$, since no term can be smaller than $0$ or larger than $1$. Since the terms get closer and closer to $0$, the limit is $0$.