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Ch. 3 - Trigonometric Identities and Equations
Blitzer - Trigonometry 3rd Edition
Blitzer3rd EditionTrigonometryISBN: 9780137316601Non è quello che usi tu?Cambia libro di testo
Capitolo 3, Problema 3.5.35

Exercises 25–38 involve equations with multiple angles. Solve each equation on the interval [0, 2𝝅). sec(3θ/2) = - 2

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Rewrite the given equation \(3\theta \sec \frac{3\theta}{2} = -2\) to isolate the secant function: \(\sec \frac{3\theta}{2} = -2\).
Recall that \(\sec x = \frac{1}{\cos x}\), so rewrite the equation as \(\frac{1}{\cos \frac{3\theta}{2}} = -2\).
Invert both sides to express in terms of cosine: \(\cos \frac{3\theta}{2} = -\frac{1}{2}\).
Find all angles \(\alpha = \frac{3\theta}{2}\) in the interval \([0, 3\pi)\) (since \(\theta \in [0, 2\pi)\), multiplying by \(\frac{3}{2}\) extends the interval) where \(\cos \alpha = -\frac{1}{2}\).
Solve for \(\theta\) by isolating it: \(\theta = \frac{2}{3} \alpha\), and then select all solutions for \(\theta\) that lie within \([0, 2\pi)\).

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Multiple-Angle Trigonometric Equations

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Secant Function and Its Properties

The secant function, sec(θ), is the reciprocal of cosine, defined as sec(θ) = 1/cos(θ). Understanding its domain, range, and behavior is essential, especially since sec(θ) can be undefined where cosine is zero, and it can take values less than -1 or greater than 1.
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Solving Trigonometric Equations on a Restricted Interval

When solving equations on [0, 2π), it is important to find all solutions within one full rotation of the unit circle. This involves considering the periodicity of the trigonometric functions and adjusting solutions for multiple angles accordingly.
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