#### Answer

$y$ is NOT a function of $x$

#### Work Step by Step

Solve for $y$.
Add $-x^2$ on both sides of the equation to obtain:
$y^2=-x^2+25$
Take the square root of both sides to obtain:
$y=\pm \sqrt{-x^2+25}$
Note that when you assign any 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 $x$.