Unit circle Angle In the field of angle, specifically in trigonometry, a unit circle refers to a circle with a radius of 1 centered at the origin (0, 0) of a coordinate plane. The unit circle is a powerful tool used for visualizing and solving trigonometric problems, as well as understanding the relationship between angles and their corresponding coordinate values on a two-dimensional plane. When an angle is represented on the unit circle, it is measured in radians or degrees, starting from the positive x-axis and rotating counterclockwise for positive angles, or clockwise for negative angles. The coordinates of a point on the unit circle represent the cosine and sine of the angle formed by the line segment connecting the origin to that point. In other words, if the angle is θ, the coordinates can be expressed as (cos(θ), sin(θ)). The unit circle aids in establishing important trigonometric functions and relationships, such as sine, cosine, and tangent, as well as their inverses, for any given angle. By using the unit circle, we can also understand periodic behavior of trigonometric functions and how they are related to angle measurement, allowing for simplification and analysis of trigonometric expressions and equations.