question_answer

Find the value of \[cos\,12{}^\circ +cos\text{ }84{}^\circ +cos\text{ }132{}^\circ +\text{ }cos\text{ }156{}^\circ .\]

A)  1                                

B)  \[-\,1\]

C)  \[\frac{1}{2}\]                         

D)  \[\frac{-1}{2}\]

E)  None of these