Addition Formulas

Sine and Cosine of Sum of Two Angles

Sometimes we encounter situations where the sin and cos of two separate angles are known and we need to find the sin or cos of the sum of the given angles. In this situation, we use the following formulas:

sin (a + b) = (sin a)(cos b) + (sin b)(cos a) 
cos (a + b) = (cos a)(cos b) – (sin a)(sin b)