**Title:** Interactive Unit Circle

**Description:**
This is an interactive model of the Unit Circle. Features include a moveable slider to change the values of central angles in radian measure.

**Standard(s): **

[MA2013] ALT (9-12) 37: Understand radian measure of an angle as the length of the arc on the unit circle subtended by the angle. [F-TF1]

[MA2013] ALT (9-12) 38: Explain how the unit circle in the coordinate plane enables the extension of trigonometric functions to all real numbers, interpreted as radian measures of angles traversed counterclockwise around the unit circle. [F-TF2]

[MA2013] ALT (9-12) 39: Define the six trigonometric functions using ratios of the sides of a right triangle, coordinates on the unit circle, and the reciprocal of other functions. (Alabama)

[MA2013] PRE (9-12) 30: (+) Use the unit circle to explain symmetry (odd and even) and periodicity of trigonometric functions. [F-TF4]