Trig Product to Sum Identities
For angles α and β, the following sum to product identities may be applied:
(1) cos(α) cos(β) = ½[cos(α + β) + cos(α − β)]
(2) sin(α) sin(β) = ½[cos(α −β) − cos(α + β)]
(3) cos(α) sin(β) = ½[sin(α + β) − sin(α − β)]
(4) sin(α) cos(β) = ½[sin(α + β) + sin(α −β)]
Other Trigonometric Identities:
- Reciprocal Identities
- Pythagorean Identities
- Even-Odd Identitites
- Cofunction Identities
- Half-Angle Identities
- Double-Angle Identities
- Sum and Difference Identities
- Sum to Product Identities