Unit Circle
In some other lessons, we have covered the three common trigonometry functions sine, cosine and tangent using the basic SOHCAHTOA 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 centre 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.
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