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 Depdendent Variable

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 Dependent Variable

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# Vertical Line Test

You have seen that a function is a rule that assigns to each input number, x, exactly one output number, y. If a rule assigns more than one output value to a given input value then it is not a function.

If we are given a graph we can determine if it represents a function by using the vertical line test.

Procedure â€” To Determine if a Graph Represents a Function (Vertical Line Test)

If you can draw a vertical line anywhere through the graph and it intersects the graph only one time, then the graph represents a function.

Here are the graphs of four functions. Notice that no matter where you draw a vertical line, it will never cross the graph more than one time.

The graphs below do NOT represent functions. In each, we can draw a vertical line that intersects the graph more than once. This shows that a given value of the input, x, is assigned to more than one value of the output, y.