Answer & Step-by-step explanation:
The vertical line test is used to determine if a given relation is a function.
How it works:
You can use anything that has a straight edge, usually a pencil. Hold it up to the graph at multiple points vertically.
Now, if the pencil crosses over two points, the relation is not a function. If you hold the pencil to the graph and it doesn't cross over two points, then the relation is a function.
If you hold a pencil to the graph vertically at each given point, the pencil does not cross over two points. Therefore, the relation is a function.
:Done