Answer:
-sin(u)
Step-by-step explanation:
This is a Trig identity. The best way to understand this is to start at zero degrees. +u would move counterclockwise, while -u moves clockwise. The sine function gives you how far in the y-direction you are from the x-axis. Since you're moving the same amount by going u degrees (or u radians) around the circle as you would going -u degrees (or -u radians), your distance from the x-axis is the same. But it reflects over the x-axis, so the two outcomes are inverses of each other.
