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Unit Circle



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More Lessons for Trigonometry

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In some other lessons, we have covered the three common trigonometry functions sine, cosine and tangent using the basic SOH-CAH-TOA definition.

In this lesson, we will extend the definition of the trigonometry functions by using the unit circle.

A unit circle is a circle of radius one unit with its center at the origin.

Sine Function

As illustrated in the following diagram:

For a point (x, y) on the unit circle; sin θ = ⇒ sin θ = y

Cosine Function

As illustrated in the following diagram:

For a point (x, y) on the unit circle; cos θ = ⇒ cos θ = x

Tangent Function

As illustrated in the following diagram:

For a point (x, y) on the unit circle; tan θ =


Videos

Unit Circle - Angles from 0° to 360°. Angles from 0 to 2π




Unit Circle - Points (x, y) along the unit circle
The following video shows how the unit circle can be used in the definitions of sine, cosine and tangent.


 

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.

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