Question

Express the following as a function of a single angle.

cos(60) cos(-20) - sin(60) sin(-20)

Answer 1

cos(60) cos(-20) - sin(60) sin(-20) = cos (40)

Explanation:

Using the trigonometric identity rule:

`\cos(A+B) = \cos A \cos B- \sin A \sin B`

Given that:

cos(60) cos(-20) - sin(60) sin(-20)

Let A = 60 and B = -20

then;

Using identity rule:

`\cos (60) \cos (-20)- \sin (60) \sin (-20) = \cos(60+(-20)) = \cos (60-20)=\cos 40`

Therefore, the following as a function of a single angle is cos (40)