Question

Which relation is a function?

Answer 1

{(2, 3), (1, 5), (2, 7)} - NOT because 2->3 and 2->7
{(11, 9), (11, 5), (9, 3)} - NOT because 11->9 and 11->5
{(3, 8), (0, 8), (3, -2)} - NOT because 3->8 and 3->-2

{(-1, 5), (-2, 6), (-3, 7)} - YES