{(2,9), (2,-5),(-6,3), (4, -7)} this pair doesn't represent a function
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 at all. The initial set or starting set is also called the domain; the final set or arrival set is called the rank.
Since in this set two elements of the range are associated with the same element of the domain [(2,9) and (2,-5)], we can conclude that it is not a function