Trigonometry 7th Edition

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

Chapter 6 - Section 6.3 - Trigonometric Equations Involving Multiple Angles - 6.3 Problem Set - Page 340: 29

Answer

$$x=\frac{\pi}{18},\ \frac{5\pi}{18}, \ \frac{13\pi}{18},\ \frac{17\pi}{18},\ \frac{25\pi}{18},\ \frac{29\pi}{18}$$

Work Step by Step

Given $$ \sin 2x \cos x - \cos 2x \sin x=\frac{1}{2},\ \ 0\leq x<2\pi $$ Then by using $\sin(A+B)=\sin A \cos B - \cos A \sin B$ , we get \begin{align*} \sin 2x \cos x - \cos 2x \sin x&=\frac{1}{2}\\ \sin(3x)&=\frac{1}{2}\\ \end{align*} First we find all possible solutions for $x$ $$ 3x=\frac{\pi}{6}+2k\pi \ \Rightarrow x= \frac{\pi}{18}+ \frac{2k\pi}{3}$$ To find those solutions that lie in the interval $0\leq x<2\pi$ we let k take on values of 0, 1, and 2; we get $$x=\frac{\pi}{18},\ \frac{5\pi}{18}, \ \frac{13\pi}{18},\ \frac{17\pi}{18},\ \frac{25\pi}{18},\ \frac{29\pi}{18}$$
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