How to Calculate Cos a Cos b

The cosine of the sum of two angles is equal to the sum of the cosines. This formula is known as the cosine rule and it holds true for any angle. Similarly, you can also find that the cosine of difference between two angles is equal to half the product of their respective cosines. This identity can be written in algebraic notation in terms of trigonometric functions as:

cos₁ ⋅ cos₂ = (1/2) (cos₁ + cos₂) + (1/2) (cos₁ – cos₂)

correct Cos a Cos b Formula