Khan Academy
Khan Academy: Trigonometry: Sine & Cosine Identities: Periodicity
Sal finds trigonometric identities for sine and cosine by considering angle rotations on the unit circle. [6:13]
Khan Academy
Khan Academy: Trigonometry: Tangent Identities: Periodicity
Sal solves a problem by considering the periodicity of the tangent function. [4:01]
Other
Trigonometric Functions f.tf.4
In this teacher-created video, trigonometric functions are developed and explored by changing one of the angles in a right triangle. [10:57]