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Ch. 1 - Angles and the Trigonometric Functions
Blitzer - Trigonometry 3rd Edition
Blitzer3rd EditionTrigonometryISBN: 9780137316601Non è quello che usi tu?Cambia libro di testo
Capitolo 1, Problema 1.19a

Use the unit circle shown to find the value of the trigonometric function.
cos 𝜋/6

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1
Identify the angle \( \frac{\pi}{6} \) on the unit circle. This angle corresponds to 30 degrees.
Recall that the unit circle is a circle with a radius of 1 centered at the origin of the coordinate plane.
On the unit circle, the coordinates of a point corresponding to an angle \( \theta \) are \((\cos \theta, \sin \theta)\).
For \( \theta = \frac{\pi}{6} \), find the x-coordinate of the point on the unit circle, which represents \( \cos \frac{\pi}{6} \).
Use the known values from the unit circle: \( \cos \frac{\pi}{6} = \frac{\sqrt{3}}{2} \).

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Unit Circle

The unit circle is a circle with a radius of one centered at the origin of a coordinate plane. It is a fundamental tool in trigonometry, as it allows for the definition of trigonometric functions based on the coordinates of points on the circle. The x-coordinate of a point on the unit circle corresponds to the cosine of the angle, while the y-coordinate corresponds to the sine.
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Introduction to the Unit Circle

Cosine Function

The cosine function, denoted as cos(θ), represents the x-coordinate of a point on the unit circle corresponding to an angle θ measured from the positive x-axis. For angles measured in radians, such as π/6, the cosine function provides a specific value that can be derived from the coordinates of the corresponding point on the unit circle.
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Graph of Sine and Cosine Function

Reference Angles

Reference angles are the acute angles formed by the terminal side of an angle and the x-axis. They are crucial for determining the values of trigonometric functions in different quadrants. For example, the angle π/6 has a reference angle of π/6 itself, which helps in finding its cosine value directly from the unit circle.
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Reference Angles on the Unit Circle