This graph does not represent a function because it doesn't pass the vertical line test.
For a graph to represent a function, there should be only one y value for every value of x.
But from this graph, when x is 2, we have two values of y.
Which means
x y
2 3
2 -1
Therefore, this graph does not represent a function
ANSWER:
Marcel is wrong, the graph doesn't represent a function.
