Recognize equations of horizontal and vertical lines.
A graph can fail to have an x-intercept or a y-intercept, which is why the phrase “if any” was added when discussing intercepts.
Graphing a Horizontal Line
Graph y = 2.
Since y is always 2, there is no value of x corresponding to y = 0, so the graph has no x-intercept. The y-intercept is (0, 2). The graph in Figure 7, shown with a table of ordered pairs, is a horizontal line.
Graphing a Vertical Line
Graph x + 1 =0.
The x-intercept is (-1, 0). The standard form 1x + 0y = -1 shows that every value of y leads to x = – 1, so no value of y makes x = 0. The only way a straight line can have no y-intercept is if it is vertical.