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Ch. 3 - Radian Measure and The Unit Circle
Lial - Trigonometry 12th Edition
Lial12th EditionTrigonometryISBN: 9780136552161, 9780135440780, 9780136881117, 9780135440827, 9780135924891Non è quello che usi tu?Cambia libro di testo
Capitolo 4, Problema 39

Find each exact function value.
csc ( ―11π/6)

Guida verificata passo dopo passo
1
Recall that the cosecant function is the reciprocal of the sine function, so \(\csc(\theta) = \frac{1}{\sin(\theta)}\).
Identify the angle given: \(-\frac{11\pi}{6}\). Since this is a negative angle, find its positive coterminal angle by adding \(2\pi\): \(-\frac{11\pi}{6} + 2\pi = -\frac{11\pi}{6} + \frac{12\pi}{6} = \frac{\pi}{6}\).
Evaluate \(\sin\left(\frac{\pi}{6}\right)\) using known special angles. Recall that \(\sin\left(\frac{\pi}{6}\right) = \frac{1}{2}\).
Since \(\sin\left(-\frac{11\pi}{6}\right) = \sin\left(\frac{\pi}{6}\right)\) (because sine is an odd function and the angle is coterminal), the value is \(\frac{1}{2}\).
Finally, find \(\csc\left(-\frac{11\pi}{6}\right)\) by taking the reciprocal of the sine value: \(\csc\left(-\frac{11\pi}{6}\right) = \frac{1}{\sin\left(-\frac{11\pi}{6}\right)} = \frac{1}{\frac{1}{2}}\).

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Understanding the Cosecant Function

The cosecant function, csc(θ), is the reciprocal of the sine function, defined as csc(θ) = 1/sin(θ). To find csc(θ), you first determine sin(θ) and then take its reciprocal. This relationship is fundamental when evaluating cosecant values exactly.
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Graphs of Secant and Cosecant Functions

Evaluating Trigonometric Functions at Negative Angles

Negative angles in trigonometry represent clockwise rotation from the positive x-axis. The sine function is odd, meaning sin(-θ) = -sin(θ). This property helps convert negative angle values into positive ones for easier evaluation using known reference angles.
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Reference Angles and Unit Circle Values

Reference angles are the acute angles formed by the terminal side of an angle and the x-axis. Using the unit circle, you can find exact sine values for common angles like π/6, π/4, and π/3. Recognizing the reference angle for -11π/6 allows precise calculation of sine and thus cosecant.
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Reference Angles on the Unit Circle