How would I simplify this difficult trigonometric identity:
$\frac{\sin A \cos A}{\cos^2 A - \sin^2 A} = \frac{\tan A}{1-\tan^2 A}.$
I am not exactly sure what to do.
I simplified the right side to
$\frac{\frac{\sin A}{\cos A}}{1-\frac{\cos^2 A}{\sin^2 A}}$
But how would I proceed.