You can put this solution on YOUR website! Sketch the angle with measure (-2π)/3 radians. Then label its reference angle
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I don't have the means to provide a sketch for you, but I can describe what you should do which might help.
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Since given angle (-2π)/3 is negative, we should rotate π/3 radians twice in the clockwise direction. This places the reference angle in quadrant III at π/3 or 60º. This gives a standard angle of 4π/3 radians or 240º