A vertical asymptote is a vertical line that the graph of the function approaches but never intersects. They are similar to horizontal asymptotes of exponential functions studied in Algebra I. The equation of a vertical asymptote has the form x = k, where k stands for a constant value.

A horizontal asymptote is a horizontal line that the graph of the function approaches, but unlike vertical asymptotes the graph can cross horizontal asymptotes. Horizontal asymptotes help to determine the end behavior of the graph of rational functions.