Sum and Difference Identities Double Angle Identities sin(u v) sin u cos v cos u sin v sin(2u) 2sin u cos u sin(u v) sin u cos v cos u sin v cos(2u) cos2 u sin 2 u cos(u v) cos u cos v sin u sin v cos(2u) 2cos2 u 1 cos(u v) cos u cos v sin u sin v cos(2u) 1 2sin 2 u tan(u v) tan u tan v 1 tan u tan v tan(2u ) tan(u v) tan u tan v 1 tan u tan v Half Angle Identities 2 tan u 1 tan 2 u Sum to Product Formulas 1 cos u u cos 2 2 uv u v sin u sin v 2sin cos 2 2 1 cos u u sin 2 2 u v u v sin u sin v 2cos sin 2 2 1 cos u u tan 2 1 cos u uv u v cos u cos v 2cos cos 2 2 sin u u tan 2 1 cos u u v u v cos u cos v 2sin sin 2 2 u 1 cos u tan 2 sin u Product to Sum Formulas Power Reducing Formulas sin u sin v 12 [cos(u v) cos(u v)] sin 2 u 1 cos(2u ) 2 cos u cos v 12 [cos(u v) cos(u v)] cos2 u 1 cos(2u ) 2 sin u cos v 12 [sin(u v) sin(u v)] tan 2 u 1 cos(2u ) 1 cos(2u ) cos u sin v 12 [sin(u v) sin(u v)]