Answer
y is not a function of x for this equation.
Work Step by Step
This question asks whether the equation defines y as a function of x (one-to-one function)
$2x = y^4 -16$
$y^4 = 2x + 16$
$y^2 = +/- \sqrt {2x + 16}$
$y = +/- \sqrt {+/- \sqrt {2x+16}}$
For one value of x, there is more than one value of y, so y is not a function of x for this equation.