Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 6 - Section 6.3 - Trigonometric Functions of Angles - 6.3 Exercises - Page 499: 42

Answer

$\cot\theta$ = $-\frac{\sqrt {1-\sin^{2}\theta}}{\sin\theta}$ ($\sin\theta\ne0$ as $\theta$ lies in quadrant II)

Work Step by Step

We are supposed to write $\cot\theta$ in terms of $\sin\theta$ while $\theta$ lies in Quadrant II. Using ratio identity for $\cot$- $\cot\theta$ = $\frac{\cos\theta}{\sin\theta}$ ($\sin\theta\ne0$ as $\theta$ lies in quadrant II) From Pythagorean identity- $\cos\theta$ may be written as $\sqrt {1-\sin^{2}\theta}$ Therefore- $\cot\theta$ = $-\frac{\sqrt {1-\sin^{2}\theta}}{\sin\theta}$ ($\sin\theta\ne0$ as $\theta$ lies in quadrant II) Since the angle is in quadrant II, where cotangent is negative but sine is positive. The negative value of the square root is chosen to make cotangent negative.
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