Answer
vertical
Work Step by Step
If we consider a graph of a vertical line, we can use the vertical line test to determine that this is not a graph of a function. For example, we can draw another vertical line that intersects the first vertical line at every point. This tells us that a vertical line cannot be a function, as the one value of the domain (a vertical line only has one x-value) corresponds to an infinite amount of y-values, so a vertical line cannot be a function.
