Sine and cosine are two key functions in trigonometry that relate angles to the ratios of sides in a right triangle. In the context of the unit circle, the cosine of an angle gives the horizontal coordinate, while the sine gives the vertical coordinate of a point on the circle. These functions are periodic, meaning they repeat in a regular pattern every full rotation, or 360 degrees. Sine starts at zero and goes up and down in a wave-like motion, while cosine starts at one and follows a similar