Trigonify

Product to Sum

cos · cos

cos⁡αcos⁡β=12[cos⁡(α−β)+cos⁡(α+β)]\cos\alpha \cos\beta = \tfrac{1}{2}[\cos(\alpha-\beta) + \cos(\alpha+\beta)]

Related Product to Sum identities

sin · cossin · sin

Study this and 44 more identities in the Trigonify workspace — an interactive unit circle, a step-by-step triangle solver, quizzes, and a practice problem bank.