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