Determine if the relation is a function and explain. a. {(-5,2), (-2,5), (0,7), (0,9)}

By definition we have to:
 A mathematical function is a relationship that is established between two sets, through which each element of the first set is assigned a single element of the second set or none.
 The initial set or starting set is also called the domain; the final set or set of arrival, meanwhile, can be called codomain.
 We have the following information:
 {(-5.2), (-2.5), (0.7), (0.9)}
 The data does not represent a function because two different values of the range belong to an element of the domain:
 (0.7)
 (0.9)
 
 The relation is not a function.