My point was that it looks like it has imaginary solutions. There may be some trig identity, look for one. Otherwise, let $\displaystyle u=\tan(x)$ attempt to solve $\displaystyle u^3-9u^2-3u+3=0$ and go from there.
My point was that it looks like it has imaginary solutions. There may be some trig identity, look for one. Otherwise, let $\displaystyle u=\tan(x)$ attempt to solve $\displaystyle u^3-9u^2-3u+3=0$ and go from there.