What is the exact value of cos 150°

-√3/2

Step-by-step explanation:

Since our angle is greater than 90, it lies in the second quadrant.

150 is obtuse angle as it is greater than 90.

We know that 150° = 180° - 30°

Also, cos (180-x) = - cos (x) because cosx is negative in the second quadrant.

cos (30) = √3/2

cos (150) = cos (180 - 30) = - cos (30) = - √3/2

OR

It can be written as:-

cos (150) = sin (90 - 150) = sin (-60) = - sin (60) = - √3/2.