z \in ℝ , didn't want it to get mixed up with x
What does it simplify to using the half-angle formulae? Using the previously stated identities it should be possible to simplify the expression inside the logarithm to tan(x/2)
EDIT: That's tan^2(x), not tan(x)!
Well, given that tan^2(u)=sin^2(u)/cos^2(u) , shouldn't it be possible to rewrite the equation into tan^2(z) , seeing as we have:
sin^2(u) = 1/2 - 1/2 cos(2u)
cos^2(u) = 1/2 + 1/2 cos(2u)