Answer: C log 16
The last step is Evaluating the Solution
(C) sin(-r) = -a
(D) sin(r) = -a
The unit circle definition allows us to extend the domain of sine and cosine to all real numbers. The process for determining the sine/cosine of any angle θ is as follows:
Starting from (1,0) move along the unit circle in the counterclockwise direction until the angle that is formed between your position, the origin, and the positive x-axis is equal to θ.
In the question, sin(-r) = -a and sin(r) = -a is equal to the x-coordinate, thus they are not correct.
An image is attached for reference.