Find the value of $\cos \left(-120°\right)$

The trigonometric function cos 120 represents the cosine of 120 degrees. To find the value of cos 120, we can analyze its position on the unit circle.

Step-by-Step Explanation

• The angle 120° lies in the second quadrant of the unit circle, where the cosine function is negative.
• The reference angle for 120° is 180° - 120° = 60°.
• The cosine of 120° is the same as the cosine of 60° in magnitude but negative because of the quadrant.
• The value of cos 60° is 1/2, so cos 120 is -1/2.

Final Answer

The value of cos 120 is -½.