Find the Value Using the Unit Circle cos(-120 degrees )

$\cos (- 120 °)$

Find the value using the definition of cosine.

$\cos (- 120 °) = \frac{adjacent}{hypotenuse}$

Substitute the values into the definition.

$\cos (- 120 °) = \frac{- \frac{1}{2}}{1}$

Divide $- \frac{1}{2}$ by $1$ .

$- \frac{1}{2}$