Question

Relation or Function ? Explain
{(2, 15), (15, –4), (–9, –7), (13, 14)}

Answer 1

it is certainly a relation because it is a set of ordered pairs. to check to see if it is a function, look at the first numbers
{2,15,-9,13}
as long as they do not repeat, it is also a functions

Answer 2

in other words if all the first numbers are different it is a function

Answer 3

A definition of a function is that "for every x, there is a unique y". For example, if (2, -1) was also in the set, it would no longer be a function. Now we have y=15 and y=-1, when x=2. This is why you need to look at the first number (x).