sample answer: you can determine whether each element of the domain is paired with exactly one element of the range. for example, if given a graph, you could use the vertical line test; if a vertical line intersects the graph more than once, then the relation that the graph represents is not a function.
![Is the relation shown a function? use the vertical line test, explain](/tpl/images/02/00/0DacCvHhNbAidIiv.jpg)