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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 44

In Exercises 44–48, find the reference angle for each angle.
265°

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1
Identify the quadrant in which the angle 265° lies. Since 265° is between 180° and 270°, it is in the third quadrant.
Recall that the reference angle is the acute angle formed between the terminal side of the given angle and the x-axis.
For angles in the third quadrant, the reference angle \( \theta_r \) is found by subtracting 180° from the given angle: \( \theta_r = \theta - 180^\circ \).
Substitute the given angle into the formula: \( \theta_r = 265^\circ - 180^\circ \).
Simplify the expression to find the reference angle.

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Reference Angle

A reference angle is the acute angle formed between the terminal side of a given angle and the x-axis. It is always positive and less than or equal to 90°, used to simplify trigonometric calculations by relating any angle to an angle in the first quadrant.
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Reference Angles on the Unit Circle

Standard Position of an Angle

An angle in standard position has its vertex at the origin and its initial side along the positive x-axis. The angle is measured counterclockwise for positive angles and clockwise for negative angles, which helps determine the quadrant where the terminal side lies.
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Drawing Angles in Standard Position

Quadrants and Angle Measurement

The coordinate plane is divided into four quadrants, each spanning 90°. Knowing the quadrant of an angle helps find the reference angle by subtracting the angle from the nearest x-axis boundary (0°, 90°, 180°, 270°, or 360°), depending on the quadrant.
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Quadratic Formula