Answer
Determining if the lines are parallel compares the slope. Determining if the lines are perpendicular also compares the slope.
However, for lines to be parallel, the slopes must be the same. For two lines to be perpendicular, the slopes are multiplied.
Work Step by Step
$ y = 2x+4$ is a line (as an example). If another line has a slope of 2, then we would know the lines are parallel. However, if the slope of the other line is -1/2, then we would know the lines are perpendicular.
