Answer
$y$ is NOT a function of $x$
Work Step by Step
Take the square root of both sides to obtain:
$\pm \sqrt{4x}=y
\\\pm2\sqrt{x}=y$
Note that when you assign any positive real number value to $x$, the equation will give two values of $y$.
Thus, the given equation does not represent $y$ as a function of $x$.
