Suppose, for the sake of keeping things as simple as possible, that I have the following equation that I wish to simplify in Mathematica:
$y = x x$
But suppose further that I also have a restriction, not directly on $x$, but on what values $y$ can have. More specifically, let's suppose $y \leq 9$.
What Mathematica expression, if any, will allow me to simplify the above expression for $y$ and get an output that not only simplifies, but also gives me the range of values that $x$ can take to satisfy my restriction on $y$?
So, just to be clear, the function or script I am looking for will output something like the following when dealing with the above:
y = $x^2$ and $-3\leq x\leq3$