I have the following equation, and I want to solve for $\theta$ :
$f(x,y,\theta) = \frac{x \cos(\theta) - y \sin(\theta)}{x \sin(\theta) + y \cos(\theta)}$
It seems to me this equation should be easily solvable given known $x$ and $y$, however I cannot find it. Any help/hints?
EDIT: There was an error in my equation. I also must add that I know the value of $f$. Currently working on it with the tip given by Chandrasekhar.
It is important to note that $\theta$ and $x$, $y$ are not related. Yes it can be seen as a rotation... (or the division of the two terms from a rotation).