A particular type of line is a vertical line. A vertical line is parallel to the y-axis and perpendicular to the x-axis. The figure below shows several vertical lines, the vertical lines are red, and the axis is black.
If we were to select two points on any of the vertical lines, we would find that while the y coordinates for the two points are different, the x coordinate for both of the points is the same. Because of this, the slope of this type of line is considered to be undefined.
We’ll select two points on a vertical line, (x, y1) and (x, y2), and with these two points, we will compute the slope of the line. Using the slope equation:
Plugging our coordinates into the equation:
We can simplify this down by subtracting the x from the x, which gives us 0.