Horizontal and Vertical Lines
The graph of a linear equation, Ax + By = C, where A and B are
not both 0, is a straight line.
â€¢ If A = 0, then the graph is a horizontal line.
For example, y = 3 is a
horizontal line. On this line, the ycoordinate is always 3.
â€¢ If B = 0, then the graph is a vertical line.
For example, x = 5 is a
vertical line. On this line, the xcoordinate is always 5.
Example 1
Graph the following linear equations:
a. y = 4
b. x = 4
Solution
a. The graph of y = 4 is a horizontal line.
On this line, the ycoordinate is always 4.
The yintercept is (0, 4); the line has no xintercept. 

b. The graph of x = 4 is a vertical line.
On this line, the xcoordinate is always 4.
The xintercept is (4, 0); the line has no yintercept. 

