2/3 Your friend is confused with finding the value of sec (). The answer your friend shared with you is . Explain any errors that were made by your friend and then explain how to find the correct answer.

Trigonometry (11th Edition)
11th Edition
ISBN:9780134217437
Author:Margaret L. Lial, John Hornsby, David I. Schneider, Callie Daniels
Publisher:Margaret L. Lial, John Hornsby, David I. Schneider, Callie Daniels
Chapter1: Trigonometric Functions
Section: Chapter Questions
Problem 1RE: 1. Give the measures of the complement and the supplement of an angle measuring 35°.
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**Problem Explanation:**

Your friend is confused with finding the value of \( \sec^{-1}\left(-\frac{2\sqrt{3}}{3}\right) \). The answer your friend shared with you is \( -\frac{\pi}{6} \).

**Task:**

1. Explain any errors that were made by your friend.
2. Explain how to find the correct answer.

**Analysis and Correct Solution:**

1. **Understanding the Secant Inverse Function:**
   - The secant inverse function, \( \sec^{-1}(x) \), gives the angle \( \theta \) such that \( \sec(\theta) = x \).
   - The range of \( \sec^{-1}(x) \) is \([0, \pi]\), excluding \( \frac{\pi}{2} \).

2. **Evaluating Errors:**
   - The value \( -\frac{\pi}{6} \) is not in the range \([0, \pi]\).
   - A negative angle like \(-\frac{\pi}{6}\) cannot be the correct principal value since it is not within the defined range of the secant inverse function.

3. **Correct Approach:**
   - Recognize that \( \sec(\theta) = \frac{1}{\cos(\theta)} \), so we solve \( \frac{1}{\cos(\theta)} = -\frac{2\sqrt{3}}{3} \).
   - Rearrange to find \( \cos(\theta) = -\frac{\sqrt{3}}{2} \).
   - Determine the angles where \( \cos(\theta) = -\frac{\sqrt{3}}{2} \) within the range \([0, \pi]\).
   - This occurs at \( \theta = \frac{5\pi}{6} \).

4. **Conclusion:**
   - The correct value of \( \sec^{-1}\left(-\frac{2\sqrt{3}}{3}\right) \) is \( \frac{5\pi}{6} \).
Transcribed Image Text:**Problem Explanation:** Your friend is confused with finding the value of \( \sec^{-1}\left(-\frac{2\sqrt{3}}{3}\right) \). The answer your friend shared with you is \( -\frac{\pi}{6} \). **Task:** 1. Explain any errors that were made by your friend. 2. Explain how to find the correct answer. **Analysis and Correct Solution:** 1. **Understanding the Secant Inverse Function:** - The secant inverse function, \( \sec^{-1}(x) \), gives the angle \( \theta \) such that \( \sec(\theta) = x \). - The range of \( \sec^{-1}(x) \) is \([0, \pi]\), excluding \( \frac{\pi}{2} \). 2. **Evaluating Errors:** - The value \( -\frac{\pi}{6} \) is not in the range \([0, \pi]\). - A negative angle like \(-\frac{\pi}{6}\) cannot be the correct principal value since it is not within the defined range of the secant inverse function. 3. **Correct Approach:** - Recognize that \( \sec(\theta) = \frac{1}{\cos(\theta)} \), so we solve \( \frac{1}{\cos(\theta)} = -\frac{2\sqrt{3}}{3} \). - Rearrange to find \( \cos(\theta) = -\frac{\sqrt{3}}{2} \). - Determine the angles where \( \cos(\theta) = -\frac{\sqrt{3}}{2} \) within the range \([0, \pi]\). - This occurs at \( \theta = \frac{5\pi}{6} \). 4. **Conclusion:** - The correct value of \( \sec^{-1}\left(-\frac{2\sqrt{3}}{3}\right) \) is \( \frac{5\pi}{6} \).
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