If cos 60^\circ = 1/2, which of the following angle has cosine of -1/2?
A
30o
B
120o
C
150o
D
210o
E
300o
Verified Correct Answer: B.
Step-by-Step Mathematical Solution
cos 60^\circ = 1/2, cos(180^\circ - 60^\circ) = -1/2
cos120^\circ = -1/2
Source: Myschool Past Questions Archive (Record #22025)