$\displaystyle 3960\,\arctan \left( {\frac {2255}{12}}\,{\frac {1}{\sqrt {-13530\,c}}

} \right) {\frac {1}{\sqrt {-13530\,c}}}=17

$

Assuming c is negative.

Okay, I've been working on this for some time now. The equation is part of a bigger problem. I just need a value for c. I know it's about -2.5 by using a numerical method. Does anyone see how this could be solved algebraically?

Thanks