Answer:
540 degrees
Step-by-step explanation:
The cosine of an angle on a unit circle yields the x value. Therefore, wherever the x value is -1, cos O is -1. Cosine is equal to -1 at 180 degrees, and every 360 degree interval after that. Since 180 degrees is not an option, we need to try the next interval of 360. 180+360=540 degrees, which is one of the options. Hope this helps!
