A vertical line is one that is parallel to the y-axis of a graph. A vertical line is also perpendicular to the x-axis of the same graph, which means that the value of the x-coordinate for a vertical line does not change.
A vertical line can be verified by checking the x-coordinate of that particular line. Any vertical line has the same value of x-coordinate throughout, which means that any two points on that line will have the same value of x-coordinate. When drawing a vertical line, you should get the value of x-coordinate for the line by putting the value of y as 0 in the equation of the line to get the x-intercept of the line. After getting the value of the x-coordinate, simply mark that point on the x-axis and then draw a straight line perpendicular to the y-axis to this point. Such a line will be parallel to the y-axis of the graph and, therefore, according to the definition of vertical lines, will be a vertical with respect to this graph. A vertical line has no slope, which can easily be proved as the value of x-coordinate of the line is same all along its path.