Answer
y is a function of x; it passes the vertical line test.
Work Step by Step
First rearrange the function to solve for y: y = $16-x^{2}$
In this case we have only one equation for y which means a single value of y will have one solution for each x. This agrees with the definition of the function, therefore y is a function of x.
You should also recognize that this is a quadratic equation and know that all such equations are functions.
