posted by Patricia .
Why is the line x=4 a vertical line?
The equation x=4 refers to all ordered pairs whose x value is 4. Thus, for example, (4,o), (4,1), (4,2), etc. all satisfy the given equation. Notice that the three ordered pairs above fall on the vertical line passing through 4 on the x-axis. Indeed, all ordered pairs on such vertical line have x coordinate =4.
Thanks a million!