The graph of a relation of the form y = 5 is a line parallel to the x-axis because the y value never changes. A line parallel to the x-axis is called a horizontal line. The graph of a relation of the form x = 5 is a line parallel to the y-axis because the x value never changes. A line parallel to the y-axis is called a vertical line. Plot the graph of each of the following relations: horizontal line, vertical line.