Answer
$\text{$y$ is NOT a function of $x$.}$
Work Step by Step
For an equation to be a function: any input $x$ will yield only one output $y$
We start by solving the equation for $y$
Rearranging the equation:
$$4y^2=x^2-1$$
Dividing both sides by $4$:
$$y^2=\dfrac{x^2-1}{4}$$
Taking the square root of both sides:
$$y = \pm \sqrt{\dfrac{x^2-1}{4}}$$
If $x=0$
$$y = \pm \sqrt{\dfrac{3^2-1}{4}} = \pm \sqrt{2}$$
As there are two different outputs resulting from the same input, the equation isn't a function
