Answer:
Explanation:
Trigonometric identities are used to show the equality of expressions involving trigonometric functions. These trigonometric functions are the sine, the cosine, and the tangent as well as their respective reciprocals which are cosecant, the secant, and the cotangent,
Some trigonometric identities are:
tanθ = sinθ / cosθ; secθ = 1 / cosθ; cosecθ = 1 / sinθ; cotθ = 1 / tanθ = cosθ / sinθ
The angle addition formula for cos is given as:
cos(α + β) = cosαcosβ - sinαsinβ
Therefore:
cos(a + b) = cosacosb - sinasinb