Answer
See below.
Work Step by Step
$RHS=\frac{tan\theta}{1-tan^2\theta}=\frac{tan\theta cos^2\theta}{cos^2\theta(1-tan^2\theta)}=\frac{sin\theta cos\theta}{cos^2\theta-cos^2\theta tan^2\theta}=\frac{sin\theta cos\theta}{cos^2\theta-sin^2\theta}=LHS$