I have been given this by my teacher because i was complaining that the problems she gave in class were to easy:

B*tan(x) = C - D*cos(x)

B, C and D are known, I am trying to solve it to have a general expression for x. (0<x<pi/2)

This is driving me crazy!! I've admitted that I've been beat and have no idea how to solve it!! I've plotted it against x to check if there's a unique solution but I still have no idea how to solve it, help!!!!