Sample The vertical line test determines if one input has exactly one output on the graph. If any vertical line passes through more than one point on the graph, then the relation is not a function. Which did you include in your response? Draw vertical lines to intersect on a graph. The relation is a function if there’s only one point of intersection on a graph. The relation is not a function if there’s more than one point of intersection on a graph. The vertical line test is used to determine if each input has exactly one output.