Precalculus: Mathematics for Calculus, 7th Edition

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

Chapter 7 - Review - Exercises - Page 578: 44

Answer

$\frac{\pi}{6}$, $\frac{5\pi}{6}$

Work Step by Step

$2\cos x-3 \tan x=0$ $2\cos x-3*\frac{\sin x}{\cos x}=0$ Multiply both sides by $\cos x$: $2\cos^2 x-3\sin x=0$ $2(1-\sin^2 x)-3\sin x=0$ $2-2\sin^2 x-3\sin x=0$ $2\sin^2 x+3\sin x-2=0$ $(2\sin x-1)(\sin x+2)=0$ If $2\sin x-1=0$, then $2\sin x=1$, and $\sin x=\frac{1}{2}$. The only solutions in $[0, 2\pi)$ are $\frac{\pi}{6}$ and $\frac{5\pi}{6}$. If $\sin x+2=0$, then $\sin x=-2$. This is not possible because $\sin x$ cannot be less than -1.
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