Vertical Line Test: Determining if an Elliptical Graph Represents a Function

Question

Is the given graph a function?

00:00 Is the given graph a function?

00:05 The definition of a function is that for each X value there is one Y value

00:10 It seems that for an X value there are several Y values, therefore not a function

00:15 And this is the solution to the question

It is important to remember that a function is an equation that assigns to each element in domain X one and only one element in range Y

Let's note that in the graph:

$f(0)=2,f(0)=-2$

In other words, there are two values for the same number.

Therefore, the graph is not a function.