Unit Circle
More Lessons for Trigonometry
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The following diagram shows how the unit circle is related to sin, cos and tan. Scroll down the page for more examples and solutions on the unit circle, sine, cosine, and tangent.
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 = 
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