Answer
$\tan 4\theta$
Work Step by Step
Comparing with the Half-Angle Identity
$\displaystyle \tan\frac{A}{2}=\pm\sqrt{\frac{1-\cos A}{1+\cos A}}$,
if we define $ A=8\theta$,
the RHS equals the given expression.
So, the LHS =$ \tan 4\theta$