## Trigonometry (10th Edition)

-90$^{\circ}$ is between 3rd and 4th quadrants.
Coterminal angles always in the same quadrant with original angle, therefore -90$^{\circ}$+360$^{\circ}$=270$^{\circ}$ -90$^{\circ}$-360$^{\circ}$=-450$^{\circ}$