Question

Which relation does not represent a function?

(2, 0), (4, 6), (6, 8), (10, 6)
(-4, 2), (1, 5), (-2, 0), (1, 6)
(-5, 3), (-3, 1), (0, -4), (3, -6)
(-3, 6), (-1, 1), (0, 1), (3, 7)

Answer 1

If the x-value is repeated in the same relation, then it's not a function.

Answer 2

The second line -> (1,5) and (1,6) cannot be in a function because a function has to pass a vertical line test. If there are multiple points sharing the same x-value (as @Calcmathlete said) then it's not a function.