Respuesta :

Step-by-step explanation:

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

Answer:

Step-by-step explanation:

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

= -cos(60) = -½