A Quadrantal angle is an angle that is not in Quadrant I. Consider angle 120. You want to find cos(120) . 120 lies in quadrant II. Also, 120=180-60. So, it is enough to find cos(60) and put the proper sign. cos(60)=1/2. Cosine is negative in quadrant II, Therefore, cos(120) = -1/2.
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obtuse angle
That's a reflex angle. 0 to <90 Acute angle 90 Right angle >90 to <180 Obtuse angle 180 Straight angle >180 to <360 Reflex angle 360 called Full circle
An obtuse angle.
An angle of 213 degrees is a reflex angle
just an angle, like any other angle.