Question

How come the graph of x = 4 is a vertical line?

Answer 1

Sir, because y there is not, only x. So x is only 4 but y can be any.

Answer 2

No matter what the y-coordinate is, when it lie on the x=4. And it forms a vertical straight line like the above :|

Answer 3

Well, if you are using a coordinate pair and the only information is "x=4" then the "y" coordinate could be anything. Therefore, the line is vertical coming from the "x=4".