Answer:
-(1/6).
Step-by-step explanation:
The angle whose cosine is -1/6 can be written as arccos(-1/6).
cos (-1/6) = cos (-2npi - arccos(-1/6) where n is an integer. The terminal angles are the same. When n = 5 we have cos(-10pi - arccos(-1/6).
So cos (-1/6) = cos(-10pi - arccos(-1/6))
and therefore cos (-10pi - arccos(-1/6) = -1/6.
We can confirm this by using a scientific calculator.
