First, do you know the basic definitions and trig identities? The very first thing I recommend is writing every thing in terms of sine and cosine, using the definitions of "tangent" and "secant". Then use a trig identity to write a quadratic equation in terms or "cosine" only and, finally, solve the equation.
I see Plato got in just ahead of me and suggested writing it as a quadratic equation in "secant" rather than "cosine"! Much of a muchness.
I tried the quadratic formula way for a different problem but I didn't get the right solution:
is there a difference between writing it as a quadratic formula in sine or any of the other basic trig definitions?