Ch. 5 - Trigonometric Identities

Lial12th EditionTrigonometryISBN: 9780136552161, 9780135440780, 9780136881117, 9780135440827, 9780135924891Non è quello che usi tu?Cambia libro di testo

Lial 12th Edition

Ch. 5 - Trigonometric Identities

Problema 5.1.68

Capitolo 6, Problema 5.1.68

Write each expression in terms of sine and cosine, and then simplify the expression so that no quotients appear and all functions are of θ only. See Example 3.
csc θ - sin θ

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Recall the definition of cosecant in terms of sine: \(\csc \theta = \frac{1}{\sin \theta}\).

Rewrite the expression \(\csc \theta - \sin \theta\) by substituting \(\csc \theta\) with \(\frac{1}{\sin \theta}\), so it becomes \(\frac{1}{\sin \theta} - \sin \theta\).

To combine the terms into a single expression without quotients, find a common denominator, which is \(\sin \theta\), and rewrite the expression as \(\frac{1}{\sin \theta} - \frac{\sin^2 \theta}{\sin \theta}\).

Combine the fractions over the common denominator: \(\frac{1 - \sin^2 \theta}{\sin \theta}\).

Use the Pythagorean identity \(\sin^2 \theta + \cos^2 \theta = 1\) to replace \(1 - \sin^2 \theta\) with \(\cos^2 \theta\), resulting in \(\frac{\cos^2 \theta}{\sin \theta}\). This expression is now in terms of sine and cosine, but still has a quotient; to eliminate the quotient, express it as \(\cos \theta \cdot \frac{\cos \theta}{\sin \theta}\) or \(\cos \theta \cdot \cot \theta\), depending on the problem's requirements.

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Reciprocal Identities

Reciprocal identities relate trigonometric functions to their reciprocals, such as cosecant (csc θ) being the reciprocal of sine (sin θ). Specifically, csc θ = 1/sin θ. Understanding these identities allows rewriting expressions involving csc θ in terms of sin θ.

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Percorso guidato

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Pythagorean Identities

Expression Simplification

Simplification involves rewriting expressions to eliminate complex fractions or quotients, often by finding a common denominator or multiplying through by terms. The goal is to express the function using only sine and cosine without any division, making the expression easier to interpret or use.

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Simplifying Trig Expressions

Trigonometric Functions in Terms of θ

Trigonometric expressions should be written solely in terms of the angle θ, avoiding other variables or functions. This ensures clarity and consistency, especially when simplifying or combining functions, and helps in applying further identities or solving equations.

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Introduction to Trigonometric Functions

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Verify that each equation is an identity.

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Match each expression in Column I with its value in Column II.

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