College Algebra (10th Edition)

RECALL: (1) A function is a relation if every element of the domain (first coordinate) is paired with exactly one element of the range (second coordinate). (2) The domain of a function is the set that contains all of the first coordinates. The range of a function is the set that contains all of the second coordinates. Note that the first coordinate $4$ is paired with two different second coordinates ($-1$ and $2$). Thus, the given relation is NOT a function.