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Ch. 5 - Trigonometric Identities
Lial - Trigonometry 12th Edition
Lial12th EditionTrigonometryISBN: 9780136552161, 9780135440780, 9780136881117, 9780135440827, 9780135924891Non è quello che usi tu?Cambia libro di testo
Capitolo 6, Problema 5.46

Concept Check Suppose that sec θ = (x+4)/x.
Find an expression in x for tan θ.

Guida verificata passo dopo passo
1
Recall the trigonometric identity: \( \sec \theta = \frac{1}{\cos \theta} \).
Given \( \sec \theta = \frac{x+4}{x} \), we can express \( \cos \theta \) as \( \cos \theta = \frac{x}{x+4} \).
Use the Pythagorean identity: \( \tan^2 \theta = \sec^2 \theta - 1 \).
Substitute \( \sec \theta = \frac{x+4}{x} \) into the identity to find \( \tan^2 \theta = \left(\frac{x+4}{x}\right)^2 - 1 \).
Simplify the expression for \( \tan^2 \theta \) and then take the square root to find \( \tan \theta \).

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Secant Function

The secant function, denoted as sec θ, is the reciprocal of the cosine function. It is defined as sec θ = 1/cos θ. In this context, sec θ = (x+4)/x implies a relationship between the angle θ and the variable x, which can be used to derive other trigonometric functions.
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Graphs of Secant and Cosecant Functions

Pythagorean Identity

The Pythagorean identity states that for any angle θ, the relationship sin² θ + cos² θ = 1 holds true. This identity can be rearranged to express tan θ in terms of sec θ, as tan² θ = sec² θ - 1. Understanding this identity is crucial for deriving tan θ from sec θ.
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Pythagorean Identities

Tangent Function

The tangent function, denoted as tan θ, is defined as the ratio of the sine and cosine functions: tan θ = sin θ/cos θ. It can also be expressed in terms of secant as tan θ = √(sec² θ - 1). This relationship allows us to find an expression for tan θ using the given sec θ value.
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Introduction to Tangent Graph