Given the question, by definition, a function is an expression, rule, or law that defines a relationship between one variable (the independent variable) and another variable (the dependent variable).
A relation can be regarded as a function if the domain (x-values) are unique, i.e, they are not repeated through out the relation.
Using question 13, the relation is a function because the set of x-values are unique. That is;
[tex]-1\ne0\ne1\ne2\text{ for the set of x-values.}[/tex]
Therefore, question 13 is a function.
