Trigonometry (10th Edition)

-159$^{\circ}$ in the III quadrant
1. Coterminal angles always in the same quadrant with original angle, because of full resolutions (2π) -159° + 360° = 201° -159° - 360° = -519° 2. 180-270 degrees in the third quadrant. Therefore 180$^{\circ}$≤201$^{\circ}$≤270$^{\circ}$ its in the third quadrant.