Step-by-step explanation:
in a function every valid values of x has exactly one assigned y value.
in an ordered pair the first number is x, the second number is y.
the y in (k, 0) is therefore 0.
and this y is different to all other y values in the relation.
therefore, k must be different to all other defined x values (otherwise it would give an x value a second y value, which would make this a not-function).
so, k must be an integer not out of {-9, 0, 2}
