IXL | Identify functions: discrete graphs

Look at this graph:

Is this relation a function?

yes

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Learn with an example

question

Look at this graph:

Is this relation a function?

yes

key idea

A relation is a function if each x-value is paired with exactly one y-value.

You can use the vertical line test on a graph to determine whether a relation is a function.

If it is impossible to draw a vertical line that intersects the graph more than once, then each x-value is paired with exactly one y-value. So, the relation is a function.

If it is possible to draw a vertical line that intersects the graph more than once, then there is an x-value that is paired with more than one y-value. So, the relation is not a function.

solution

Apply the vertical line test:

The vertical red line intersects the graph in two places, so the relation is not a function.

Looking for more? Try these:

Lesson: Relations and functions

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Identify functions from ordered pairs, arrow diagrams, and tables

Lesson: Relations and functions

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