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If \( \sin \theta=-\frac{2}{3} \), which of the following are possible? Choose all correct answers. \( \sec \theta=\frac{3}{\sqrt{5}} \) and \( \tan \theta=-\frac{2}{\sqrt{5}} \) \( \sec \theta=-\frac{3}{2} \) and \( \tan \theta=\frac{2}{\sqrt{5}} \) \( \cos \theta=-\frac{\sqrt{5}}{3} \) and \( \tan \theta=\frac{2}{\sqrt{5}} \) \( \cos \theta=\frac{\sqrt{5}}{3} \) and \( \tan \theta=\frac{2}{\sqrt{5}} \)

Ask by Rose Warren. in the United States
Jan 24,2025

Real Tutor Solution

Tutor-Verified Answer

Answer

The possible answers are: - \( \sec \theta = \frac{3}{\sqrt{5}} \) and \( \tan \theta = -\frac{2}{\sqrt{5}} \) - \( \cos \theta = -\frac{\sqrt{5}}{3} \) and \( \tan \theta = \frac{2}{\sqrt{5}} \) These correspond to options A and C.

Solution

Given \( \sin \theta = -\frac{2}{3} \), we can determine the possible values for \( \cos \theta \) and \( \tan \theta \). 1. **Determine \( \cos \theta \):** \[ \sin^2 \theta + \cos^2 \theta = 1 \\ \left(-\frac{2}{3}\right)^2 + \cos^2 \theta = 1 \\ \frac{4}{9} + \cos^2 \theta = 1 \\ \cos^2 \theta = \frac{5}{9} \\ \cos \theta = \pm \frac{\sqrt{5}}{3} \] 2. **Determine \( \tan \theta \):** \[ \tan \theta = \frac{\sin \theta}{\cos \theta} = \frac{-\frac{2}{3}}{\pm \frac{\sqrt{5}}{3}} = \mp \frac{2}{\sqrt{5}} \] 3. **Determine \( \sec \theta \):** \[ \sec \theta = \frac{1}{\cos \theta} = \frac{3}{\pm \sqrt{5}} \] Now, evaluate each option: 1. **\( \sec \theta = \frac{3}{\sqrt{5}} \) and \( \tan \theta = -\frac{2}{\sqrt{5}} \):** - This corresponds to \( \cos \theta = \frac{\sqrt{5}}{3} \) and \( \tan \theta = -\frac{2}{\sqrt{5}} \). - This is consistent with \( \sin \theta = -\frac{2}{3} \) in Quadrant IV. 2. **\( \sec \theta = -\frac{3}{2} \) and \( \tan \theta = \frac{2}{\sqrt{5}} \):** - This would imply \( \cos \theta = -\frac{2}{3} \). - However, this violates the Pythagorean identity since \( \sin^2 \theta + \cos^2 \theta \neq 1 \). - **Invalid.** 3. **\( \cos \theta = -\frac{\sqrt{5}}{3} \) and \( \tan \theta = \frac{2}{\sqrt{5}} \):** - This corresponds to \( \tan \theta = \frac{2}{\sqrt{5}} \). - This is consistent with \( \sin \theta = -\frac{2}{3} \) in Quadrant III. 4. **\( \cos \theta = \frac{\sqrt{5}}{3} \) and \( \tan \theta = \frac{2}{\sqrt{5}} \):** - Given \( \sin \theta = -\frac{2}{3} \), this would imply \( \tan \theta = -\frac{2}{\sqrt{5}} \). - **Inconsistent with the given \( \tan \theta \).** **Therefore, the correct possible options are the first and third statements.** **Answer:** All except the second and fourth choices are possible.

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Bonus Knowledge

To determine the correct statements given \( \sin \theta = -\frac{2}{3} \), we first need to find \( \cos \theta \) using the Pythagorean identity: \[ \sin^2 \theta + \cos^2 \theta = 1 \] Substituting the value of \( \sin \theta \): \[ \left(-\frac{2}{3}\right)^2 + \cos^2 \theta = 1 \implies \frac{4}{9} + \cos^2 \theta = 1 \] This simplifies to: \[ \cos^2 \theta = 1 - \frac{4}{9} = \frac{5}{9} \implies \cos \theta = \pm \frac{\sqrt{5}}{3} \] Now, knowing \( \sin \theta \) is negative, we can determine that \( \theta \) is in either the third or fourth quadrant, where \( \cos \theta \) is positive or negative respectively. This leads us to possible values for \( \tan \theta \): \[ \tan \theta = \frac{\sin \theta}{\cos \theta} \] With \( \sin \theta = -\frac{2}{3} \): 1. If \( \cos \theta = \frac{\sqrt{5}}{3} \), then: \[ \tan \theta = \frac{-\frac{2}{3}}{\frac{\sqrt{5}}{3}} = -\frac{2}{\sqrt{5}} \] 2. If \( \cos \theta = -\frac{\sqrt{5}}{3} \), then: \[ \tan \theta = \frac{-\frac{2}{3}}{-\frac{\sqrt{5}}{3}} = \frac{2}{\sqrt{5}} \] Given this analysis we can evaluate which options can be correct. - First option: \( \sec \theta=\frac{3}{\sqrt{5}} \) does not hold since \( \sec \theta = \frac{1}{\cos \theta} \) and would have no valid \( \cos \theta \) that gives this secant. - Second option: \( \sec \theta=-\frac{3}{2} \) leads to \( \cos \theta = -\frac{2}{3} \), which does not match our derived cosine values. - Third option: \( \cos \theta=-\frac{\sqrt{5}}{3} \) is possible along with \( \tan \theta=\frac{2}{\sqrt{5}} \). - Fourth option: \( \cos \theta=\frac{\sqrt{5}}{3} \) holds with \( \tan \theta=-\frac{2}{\sqrt{5}} \). Thus, the correct answers are: Third option: \( \cos \theta=-\frac{\sqrt{5}}{3} \) and \( \tan \theta=\frac{2}{\sqrt{5}} \) Fourth option: \( \cos \theta=\frac{\sqrt{5}}{3} \) and \( \tan \theta=-\frac{2}{\sqrt{5}} \)

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