$Find the cosine value of the angle 120 degrees on the unit circle.$
Answer 1
Joseph Robinson
$120\ degrees\ is\ in\ the\ second\ quadrant.\ The\ reference\ angle\ is\ 180 – 120 = 60\ degrees.$
$In\ the\ second\ quadrant,\ \cos(\theta)\ is\ negative.$
$\cos(60\ degrees) = \frac{1}{2},\ so\ \cos(120\ degrees) = -\frac{1}{2}.$
Answer 2
Charlotte Davis
$120 degrees is frac{2pi}{3} radians.$
$cos(frac{2pi}{3}) can be found using the unit circle.$
$The x-coordinate of the unit circle at frac{2pi}{3} radians is -frac{1}{2}.$
$Therefore, cos(120 degrees) = -frac{1}{2}.$
Answer 3
Lucas Brown
$120 degrees is in the second quadrant.$
$The cosine of 120 degrees is the negative of the cosine of 60 degrees.$
$cos(120 degrees) = -frac{1}{2}.$
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