F-TF.A. Extend the domain of trigonometric functions using the unit circle.

• Exploring Sinusoidal Functions

F-TF.A.1. Understand radian measure of an angle as the length of the arc on the unit circle subtended by the angle.

• Bicycle Wheel
• What exactly is a radian?

F-TF.A.2. 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.

• Properties of Trigonometric Functions
• Trig Functions and the Unit Circle
• Trigonometric functions for arbitrary angles (radians)
• Trigonometric Identities and Rigid Motions

F-TF.A.3. Use special triangles to determine geometrically the values of sine, cosine, tangent for $\pi/3$, $\pi/4$ and $\pi/6$, and use the unit circle to express the values of sine, cosines, and tangent for $\pi - x$, $\pi + x$, and $2\pi - x$ in terms of their values for $x$, where $x$ is any real number.

• Equilateral triangles and trigonometric functions
• Special Triangles 1
• Special Triangles 2

F-TF.A.4. Use the unit circle to explain symmetry (odd and even) and periodicity of trigonometric functions.

• Properties of Trigonometric Functions