I have a function that I cannot seem to solve and I really need help please :( 

Given $a$ and $b$:

$a = \dfrac{b-\cos(c)}{\cos^2(c)}$ with $0 \leq c < \dfrac{\pi}{2}$

I can graph this if I just provide $b$ and use $c$ as the input variables, but I need to find a discrete answer, or answers. 

Any help would be so very much appreciated, as I'm entirely stuck :)