#### Answer

The equation of the horizontal asymptote for the function $f\left( x \right)$ is $\underline{y=0}$.

#### Work Step by Step

The vertical asymptote is a horizontal line which the function approaches but does not touch.
It is clear from the graph that the function approaches the line $y=0$ line but does not touch it.
Therefore, the equation of the horizontal asymptote is $y=0$.