<p>I know that <code>tan(angle)</code> gets me the tangent. But how do I do the "reverse tangent" so that I can get the angle given the length of both sides of the right triangle?</p>

<p>I'm assuming there is a method for this in <code>math.h</code>?</p>

There should be an atan() function.
For example:
http://www.acm.uiuc.edu/webmonkeys/book/c_guide/2.7.html