Unit Circle: The unit circle is a circle with a radius of 1 unit centered at the origin (0, 0) in the coordinate plane. It is used to define trigonometric functions and their relationships.
Angle Measure: Angle measure refers to the amount of rotation around a circle, typically measured in degrees or radians. The point (0, 1) on the unit circle corresponds to an angle of 90 degrees or $\pi/2$ radians.
Trigonometric Functions: Trigonometric functions, such as sine, cosine, and tangent, are defined using the coordinates of points on the unit circle. The point (0, 1) is the y-coordinate of the sine function at an angle of 90 degrees or $\pi/2$ radians.