Question

Which of the following sets represents a function?
{(3, 5), (-1, 7), (3, 9)}
{(1, 2), (3, 2), (5, 7)}
{(1, 2), (1, 4), (1, 6)}

Answer 1

The last one

Answer 2

That was a poor way of phrasing it on my part...

Essentially, since no two x-values are repeated in the second one, it's a function.

Answer 3

A function is a correspondence (mapping) between two sets (domain and range) such that for every element in the domain, there is exactly one corresponding element in the range. Somewhat less formally, for every x (in the domain), there is only one y (in the range). The second relation listed meets this specification.