Evaluate the following expression exactly: cosine of 120° cos(120) ​

Question

Evaluate the following expression exactly: cosine of 120°

`cos(120)`
​

Answer 1

cos(120°) = -1/2° or 0.5°

Explanation:

Answer 2

cos120° = -
`(1)/(2)`

Explanation:

note that 120° is an angle in the second quadrant where cos < 0

cos120° = - cos(180 - 120)° = - cos60° = -
`(1)/(2)`