The Vertical Line Test
The vertical Line test is a wy to determine whether or not a relation
is a function
. The vertical line test simply states that if a vertical line intersects the relation's graph in more than one place, then the relation
is a NOT a function
If you think about it, the vertical line test is simply a restatement of the the definition of a function which states that every x value must have a unique y value. Well, if any particular x value has more than one y value, then you can pass a vertical line will intersect with the graph of the relation more than once. Let's re-examine the two relations from above:
On the left are the graphs of the two relations examined above. Relation #2 does not pass the vertical line test.