Answer:
a. x-coordinate
Step-by-step explanation:
In the unit circle, the value of cosine is the x-coordinate of the unit radius.
In general, you must associate vertical axis with sine and horizontal axis with cosine. The reason of this is beacuse of trigonometric reasons, when we analyse the radius of the unit circle, we form a right triangle, where the opposite leg to the direction of the radius is Y and the adjacent leg is X. Now, remember that the sine function is opposite leg over hipothenuse, and cosine function is adjacent leg over hypothenuse, where the hypothenuse is the radius.
Therefore, the right answer is a. x-coordinate.
