Sample Response: The vertical line test is a way to determine if a relation is a function. This 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 because two different outputs have the same input. Which did you include in your response? The relation is a function if there is only one point of intersection for any vertical line on the graph. The relation is not a function if any vertical line has more than one point of intersection on the graph. The vertical line test is used to determine if one input has exactly one output.