Question

Determine whether the relation is a function {(1, -3), (1, 1), (6, -8), (9, -3), (11, -3)}

Answer 1

If the same x value gives two different y values, then it is NOT a function.

Answer 2

(1, -3) implies x = 1, y = -3
(1, 1) implies x = 1, y = 1
So when x = 1, y has two different values: -3 and 1.
Therefore, this is not a function. It fails the vertical line test. That is, in a graph, if you draw a vertical line, the line should not cross the function at two different points in a function.