Answer:
-√3/2
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.