5. Use the angle addition formula to find the expression for cos (a+b).

Step-by-step 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

step-by-step explanation:

you can add the two numbers and divide the result by 2. or you can find the gap between the two numbers and add half of this to the smaller number.