Answer
$y$ is not a function of $x$
Work Step by Step
Solve the equation for $y$:
$16x-y^4=0$
$-y^4=-16x$
$y^4=16x$
$y=±\sqrt[4] {16x}$
$y=±2\sqrt[4] x$
So, for each value of $x$ in the domain, except $x=0$, we will find 2 different values of $y$. For example, if $x=81$:
$y=±2\sqrt[4] {81}=±6$
