Answer:
c. 540°
Explanation:
You want to know which angle θ has cos(θ) = -1.
Cosine
The cosine function is periodic with period 360°. The smallest positive angle θ for which cos(θ) is -1 is 180°. The next such angle is ...
180° +360° = 540° . . . . . choice D
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Additional comment
A graph of the cosine function is attached. The horizontal axis is in degrees.
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