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Ch. 1 - Trigonometric Functions
Lial - Trigonometry 12th Edition
Lial12th EditionTrigonometryISBN: 9780136552161, 9780135440780, 9780136881117, 9780135440827, 9780135924891Non è quello che usi tu?Cambia libro di testo
Capitolo 2, Problema 67

Find the indicated function value. If it is undefined, say so. See Example 4. sec 180°

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1
Recall the definition of the secant function: \(\sec \theta = \frac{1}{\cos \theta}\).
Identify the angle given: \(180^\circ\).
Find the cosine of \(180^\circ\): \(\cos 180^\circ\).
Evaluate \(\cos 180^\circ\) using the unit circle or known values. (Note: \(\cos 180^\circ = -1\).)
Calculate \(\sec 180^\circ\) by taking the reciprocal of \(\cos 180^\circ\), i.e., \(\sec 180^\circ = \frac{1}{\cos 180^\circ}\).

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Definition of the Secant Function

The secant function, sec(θ), is the reciprocal of the cosine function: sec(θ) = 1/cos(θ). It is defined wherever cosine is not zero. Understanding this reciprocal relationship is essential to evaluate secant values for given angles.
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Graphs of Secant and Cosecant Functions

Cosine of Special Angles

Cosine values for special angles like 0°, 90°, 180°, and 270° are fundamental. For 180°, cos(180°) = -1. Knowing these values helps directly compute sec(180°) by taking the reciprocal of cosine at that angle.
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Intro to Law of Cosines

Domain and Undefined Values of Trigonometric Functions

Trigonometric functions can be undefined when their denominators are zero. Since sec(θ) = 1/cos(θ), sec(θ) is undefined where cos(θ) = 0. Recognizing these points prevents errors in evaluation and helps identify when a function value does not exist.
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Domain and Range of Function Transformations