Chapter 2 - Functions, Equations, and Graphs - 2-1 Relations and Functions - Practice and Problem-Solving Exercises - Page 66: 37

y is not a function of x

$y$ is not a function of $x$ because when it is graphed, a vertical line passes through more than one point on the line. Each x coodinate greater than $\frac{7}{3}$ corresponds with two y coordinates. Since there is more than one value in the range corresponding with each value in the domain, the relation is not a function.