Question

Trigonometry
Reference Angles and Triangles
Give an exact value for Cos 120º.

Answer 1

Explanation:

`cos \: 120 \degree \\ = cos \:( 180 \degree - 60 \degree) \\ = - cos \: 60 \degree \\ = - (1)/(2) \\ \\ \huge \purple{ \boxed{ \therefore \: cos \: 120 \degree = - (1)/(2) }} \\`

Answer 2

-½

Explanation:

cos(120) = -cos(180-120)

= -cos(60) = -½