The points on the graphs represent relations. classify these relations according to whether or not they are functions.

A function from a set to a set is a relation that assigns to each element in the set exactly one element in the set . The set is the domain (also called the set of inputs) of the function and the set contains the range (also called the set of outputs).

First figure is not a function because the x-coordinate 2 has more than one element in the set of outputs.Second figure is a function because this each element in the set is assigned to exactly one element in the set . Third figure is not a function because the x-coordinates -1, 1 and 2 have assigned more than one element in the set of outputs.Fourth figure is a function because this each element in the set is assigned to exactly one element in the set .