Answer
The equation defines $y$ is a function of $x$.
Work Step by Step
For an equation to be a function, it must satisfy the following requirement:
Every value of $x$ must correspond to exactly one value of $y$.
In this case it is true, because if we plug in any number in the place of $x$ the value of $y$ will be clear.
For example, for $x=2$, $x^2=2^2=4$, therefore $y$ can only have $4$ as a value if $x=2$.
Although it is not true the other way around, it does not matter.
For example there can be two $x$ values corresponding to $y=4$. $x=\pm2$.
This is not a requirement for a function.
