SOLUTION: Using reference angles, find the value of cos(-210)

Algebra ->  Trigonometry-basics -> SOLUTION: Using reference angles, find the value of cos(-210)      Log On


   

Question 1018463: Using reference angles, find the value of cos(-210)
Answer by fractalier(6550) About Me  (Show Source):
You can put this solution on YOUR website!
cos(-210) has a reference angle of 30 degrees and it is in quadrant II.
In QII, cosine is negative so
cos(-210) = - cos(30) =
-sqrt%283%29%2F2