Angle of measure -120° :
Let m∠XOA = – 120°
Its terminal arm (ray OA) intersects the standard unit circle at P(x, y).
Draw seg PM perpendicular to the X-axis.
∴ ΔOMP is a 30° - 60° - 90° triangle.
OP = 1,
Since point P lies in the 3rd quadrant, x < 0, y < 0
