What is inverse tangent? I recently started thinking about what inverse tangent is. It is obvious that the definition of tangent is $\frac{\sin x}{\cos x}$, however, what is inverse tangent?
I first thought $\tan^{-1} x = \frac{\sin^{-1} x}{\cos^{-1} x}$, but it didn't seem right when I graph it out.
One interesting I find is in most of the programming language I know, there are two atan functions. Does this mean there are two definition of $\tan^{-1}$?

I will not comment on a relationship between arctan and arcsine and/or arccosine., other than I do not know of anything simple or commonly known.
In common programming languages, there are two arctan functions.  $\phi=\text{atan}(y)$ is an angle whose tangent is $y$, such that $x \in (-\pi/2,\pi/2)$.  This ignores anything in the second and third quadrant.  To fix this, $\phi=\text{atan2}(x,y)$ (the arguments are sometimes reversed) is the angle whose cosine is $x$ and whose sine is $y$.  This allows the second and third quadrant to be determined at the cost of having to input the sines and cosine instead of simply the tangent.
