Trigonometry 7th Edition

Published by Cengage Learning
ISBN 10: 1111826854
ISBN 13: 978-1-11182-685-7

Chapters 1-6 - Cumulative Test - Page 358: 3

Answer

$\begin{array}{|c|c|}\hline \sin\theta = \dfrac{24}{25} \text{(given)} & \color{blue}{\csc\theta = \dfrac{25}{24}} \\ \hline \color{blue}{\cos\theta = -\dfrac{7}{25}} & \color{blue}{\sec\theta = -\dfrac{25}{7}} \\ \hline \color{blue}{\tan\theta = -\dfrac{24}{7}} & \color{blue}{\cot\theta = -\dfrac{7}{24}} \\ \hline \end{array}$

Work Step by Step

Given: $\sin\theta = \frac{24}{25},\ \theta \in {\rm QII}$ Since $\theta \in {\rm QII}$, then $\begin{array}{|c|c|}\hline \sin\theta \gt 0 & \csc\theta \gt 0 \\ \hline \cos\theta\lt 0 & \sec\theta \lt 0 \\ \hline \tan\theta \lt 0 & \cot\theta \lt 0 \\ \hline \end{array}$. (i) $\color{blue}{\csc\theta} = \dfrac{1}{\sin\theta} = \dfrac{1}{24/25} = \color{blue}{\dfrac{25}{24}}$. (ii) From $\cos^2\theta + \sin^2\theta = 1$, we have $\quad \begin{eqnarray} \cos^2\theta &=& 1-\sin^2\theta \\ &=& 1 - \left(\frac{24}{25}\right)^2 \\ &=& 1 - \frac{576}{625} \\ &=& \frac{625-576}{625} \\ &=& \frac{49}{625} \\ \cos\theta &=& \pm\sqrt{\frac{49}{625}} \\ &=& \pm \frac{7}{25} \\ \color{blue}{\cos\theta} &=& \color{blue}{-\frac{7}{25}},\quad \text{since}\ \cos\theta \lt 0\ \text{in QII}. \end{eqnarray}$ (iii) $\color{blue}{\sec\theta} = \dfrac{1}{\cos\theta} = \dfrac{1}{-7/25} = \color{blue}{-\dfrac{25}{7}}$. (iv) $\color{blue}{\tan\theta} = \dfrac{\sin\theta}{\cos\theta} = \dfrac{24/25}{-7/25} = \color{blue}{-\dfrac{24}{7}}$. (v) $\color{blue}{\cot\theta} = \dfrac{1}{\tan\theta} = \dfrac{1}{-24/7} = \color{blue}{-\dfrac{7}{24}}$. Summarizing (i)-(v): $\begin{array}{|c|c|}\hline \sin\theta = \dfrac{24}{25} \text{(given)} & \color{blue}{\csc\theta = \dfrac{25}{24}} \\ \hline \color{blue}{\cos\theta = -\dfrac{7}{25}} & \color{blue}{\sec\theta = -\dfrac{25}{7}} \\ \hline \color{blue}{\tan\theta = -\dfrac{24}{7}} & \color{blue}{\cot\theta = -\dfrac{7}{24}} \\ \hline \end{array}$
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.