Answer
Horizontal asymptotes are horizontal lines that the graph of the function approaches as x tends to +∞ or −∞. As the name indicates they are parallel to the x-axis.
Work Step by Step
By definition of Horizontal asymptotes,
If $\lim\limits_{x \to +\infty\ \&\ -\infty}f(x) = c $,
then $y=c$ is Horizontal asymptote of the function $f(x)$.
