Exercise 67 Page 66

For a relation to be a function, each $x\text{-}$value can only be paired with one $y\text{-}$value, but one $y\text{-}$value can be paired with multiple $x\text{-}$values. Let's consider the given ordered pairs.

$$\begin{array}{c}\{(8,4),(6,3),(4,2),(2,1),(6,0)\}\end{array}$$

Examining the ordered pairs, we can see that $6$ is an $x\text{-}$value that is connected to two different $y\text{-}$values, which are $3$ and $0.$ Therefore, the relation is not a function.