find cos 150 degrees

Answer 1

First, we need to determine which quadrant the angle lies in order to determine if it is positive or negative. 150° is less than 180° and greater than 90°, so this puts the angle in Quadrant II and cosine is negative in Quadrant II. Second, we need to determine the reference angle in order to find the value of cosine. The reference angle is the angle between the horizontal (180°) and the angle given (150°), which would be 180°-150°=30°. The cosine of 30° = (√3)/2 and because it is in Quadrant II it is negative, so the answer is

-(√3)/2.

Hope this helps!

Answer 2

150° has a reference angle of 30°. So the value would be the same as cos 30 = √3/2

Since it is in the 2nd quadrant, cos is negative. So the answer is

cos 150° = -√3/2