A horizontal asymptote is similar to a vertical asymptote, but it is associated with the y axis. For example, for the function

gives a solution of:

and, thus, the implied limit is:

This is because we know that:

And as x gets larger (or closer to ±∞) the points on the graph come closer to the horizontal line y = 2 (seen as a dashed line on the graph on page 225), which is called the horizontal asymptote.

Four examples of graphed equations limited by vertical asymptotes.