Trigonometry (10th Edition)

Published by Pearson
ISBN 10: 0321671775
ISBN 13: 978-0-32167-177-6

Chapter 6 - Inverse Circular Functions and Trigonometric Equations - Section 6.2 Trigonometric Equations I - 6.2 Exercises - Page 267: 57

Answer

The solutions to this problem is $\theta=$ {$45^\circ+n\pi, n\in Z$} or $\theta=$ {$108.4349^\circ+n\pi, n\in Z$}

Work Step by Step

$$\frac{2\tan\theta}{3-\tan^2\theta}=1$$ Since the left side is a fraction, we must build up some conditions first. *Conditions: $$3-\tan^2\theta\ne0$$ $$\tan^2\theta\ne3$$ $$\tan\theta\ne\pm\sqrt 3$$ After building the conditions, we can solve the equation now. $$\frac{2\tan\theta}{3-\tan^2\theta}=1$$ Multiply both sides by $3-\tan^2\theta$, we have $$2\tan\theta=3-\tan^2\theta$$ $$\tan^2\theta+2\tan\theta-3=0$$ $$\tan^2\theta-\tan\theta+3\tan\theta-3=0$$ $$\tan\theta(\tan\theta-1)+3(\tan\theta-1)=0$$ $$(\tan\theta-1)(\tan\theta+3)=0$$ $$\tan\theta=1$$ or $$\tan\theta=-3$$ *For $\tan\theta=1$, $\theta=45^\circ$ A full set of values of $\theta$ therefore would be {$45^\circ+n\pi, n\in Z$} *For $\tan\theta=-3$, $\theta=-71.565^\circ$ To eliminate the negative sign, we can add $180^\circ$ to the result, making it $\theta=108.4349^\circ$ A full set of values of $\theta$ therefore would be {$108.4349^\circ+n\pi, n\in Z$}
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