Trigonometry 7th Edition

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

Chapter 1 - Section 1.4 - Introduction to Identities - 1.4 Problem Set - Page 40: 40

Answer

$\\cot\theta$ = - $\frac{\sqrt 5}{2}$

Work Step by Step

To find $\cot\theta$, we will calculate $\cos\theta$ first- We know from first Pythagorean identity that- $\cos\theta$ = ± $\sqrt (1-\sin^{2}\theta)$ As $\theta$ terminates in Q II, Therefore $\cos\theta$ will be negative- $\cos\theta$ = - $\sqrt (1-\sin^{2}\theta)$ substitute the given value of $\sin\theta$- $\cos\theta$ = - $\sqrt (1-(\frac{2}{3})^{2})$ $\cos\theta$ = - $\sqrt (1-\frac{4}{9})$ $\cos\theta$ = - $\sqrt (\frac{9 - 4}{9})$ = $\sqrt (\frac{5}{9})$ $\cos\theta$ = - $\frac{\sqrt 5}{3}$ By ratio identity- $\cot\theta$ = $\frac{\cos\theta}{\sin\theta}$ Substituting the values of $\cos\theta$ and $\sin\theta$- $\\cot\theta$ = $\frac{-\sqrt 5/3}{2/3}$ = - $\frac{\sqrt 5}{2}$
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