## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

This set of ordered pairs represents a function. Domain: $\left\{1,2,3,4\right\}$ Range: $\left\{3\right\}$
According to the definition of a function, one first element must be paired with exactly one value from the second set. In this case, this is true for all pairs. The domain contains all values from the first set of the function: Domain: $\left\{1,2,3,4\right\}$ The range contains every value from the second set that are paired with elements from the first set: Range: $\left\{3\right\}$ ** Notice: this element from the second set ("3"), is paired with more than one element from the first set, but that is totally fine. But, in a function, the reverse can't happen (a first element paired with more than one second element).