Chapter 1 - Functions and Their Graphs - Section 1.1 Functions - 1.1 Assess Your Understanding - Page 54: 33

$\text{$y$ is NOT a function of $x$.}$

For an equation to be a function: any input $x$ will yield only one output $y$ We start by solving the equation for $y$ Taking the square root of both sides: $$y = \pm \sqrt{x}$$ If $x=4$ $$y = \pm \sqrt{4} = \pm 2$$ As there are two different outputs resulting from the same input, the equation isn't a function