Unit Circle

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 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 =

The following video shows how the unit circle can be used in the definitions of sine, cosine and tangent.

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