Verify the Given Identity $$\frac { \sin u + \sin v } { \cos u + \cos v } = \tan \frac { 1 } { 2 } ( u + v )$$

Essay

Verify the given identity.
$$\frac { \sin u + \sin v } { \cos u + \cos v } = \tan \frac { 1 } { 2 } ( u + v )$$