$$\left. \begin{array} { l } { \frac { 1 + \cos 2 A } { \sin 2 A } = \cot A } \\ { \frac { \cot A - \tan A } { \cot A + \tan A } = \cos 2 A } \\ { \frac { \sin 2 A + \sin A } { \sin 2 A + \sin A } } \end{array} \right.$$
