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Videos, worksheets, games and activities to help Algebra II students learn the unit circle definition of trigonometric function.

The Definitions of Sine and Cosine :

The right triangle definitions of sine and cosine only apply to acute angles, so a more complete definition is needed. The point where the terminal side intersects the unit circle (x, y) is the basis for this definition. Since the radius (and therefore hypotenuse of the right triangle) is 1, the denominators cosine = adjacent/hypotenuse and sine = opposite/hypotenuse are also 1. Thus, the definition is y = sine and x = cosine.

Unit Circle Definition of Trig Functions

Using the unit circle to define the sine, cosine, and tangent functions

Using the unit circle to extend the SOH CAH TOA definition of the basic trigonometric functions.

This video shows how to derive the values in the first quadrant of the unit circle.

This video shows a little 'trick' to remember the values on the unit circle in the first quadrant.

You can use the Mathway widget below to practice Algebra or other math topics. Try the given examples, or type in your own problem. Then click "Answer" to check your answer.