## Answer

{(3, 2), (6, 4), (9, 6), (12, 8)} **is** a function

{(2, 3), (2, 5), (3, 6), (9, 4)} is **not** a function

{(2, 4), (6, 3), (4, 8), (6, 6)} is **not** a function

{(3, 4), (5, 2), (6, 8), (6, 4)} is **not** a function

## Explanation

To test if a relation is a function from a set of ordered pairs, you just need to check if each element of the domain is paired with **exactly **one element of the range. Remember that the domain is all the x-values (first points of each ordered pairs) and the range is all the y-values (second points of each ordered pairs).

Let’s test each one of our relations:

{(3, 2), (6, 4), (9, 6), (12, 8)} each element of the domain is paired with exactly one element of the range, so this one is a function.

{(2, 3), (2, 5), (3, 6), (9, 4)} 2 in the domain is paired with both 3 and 5 in the range, so this one is not a function.

{(2, 4), (6, 3), (4, 8), (6, 6)} 6 is paired with both 3 and 6, so this one is not a function either.

{(3, 4), (5, 2), (6, 8), (6, 4)} 6 is paired with both 8 and 4, so this one is not a function either.