Question

How do you evaluate `cos(pi+pi/3)`?

Answer 1

(- 1/2)

Explanation:

Use the trig identity:
cos (a + b) = cos a.cos b - sin a.sin b
`cos (pi + pi/3) = cos pi.cos (pi/3) - sin pi.sin (pi/3)`
Trig table of special arcs -->
`cos pi = - 1` and `cos (pi/3) = 1/2`
`sin pi = 0`
`cos (pi + pi/3) = (-1)(1/2) = - 1/2`