The unit circle is a circle with a radius of 1, centered at the origin of a coordinate plane. It plays a central role in trigonometry because every point on the unit circle corresponds to an angle and its sine and cosine values. If you take an angle measured from the positive x-axis, the coordinates of the point where the terminal side of that angle intersects the circle are exactly (cos θ, sin θ). This makes the unit circle a powerful tool for understanding the behavior of trigonometric functio