You can put this solution on YOUR website! What reference angle in the first quadrant corresponds to theta=-120? Answer in radians.
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The reference angle is the angle between the given angle
and the closest segment of the horizontal axis.
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Your problem.
-120 is in the 3rd Quadrant and is 60 degrees from the x-axis.
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Ans: 60 degrees or pi/3
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Cheers,
Stan H.