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.

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.

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.

Use vertical line test

A relation passing vertical line test is a function

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.

Use vertical line test

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.

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.

vertical line test is used to check if a curve is a function or not.