Precalculus: Mathematics for Calculus, 7th Edition

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

Chapter 7 - Section 7.2 - Addition and Subtraction Formulas - 7.2 Exercises - Page 551: 32

Answer

$\cos(x+\frac{\pi}{3})+\sin(x-\frac{\pi}{6})=0$

Work Step by Step

Start with the left side: $\cos(x+\frac{\pi}{3})+\sin(x-\frac{\pi}{6})$ Expand using the addition formula for cosine and the subtraction formula for sine: $=(\cos x\cos \frac{\pi}{3}-\sin x\sin \frac{\pi}{3})+(\sin x\cos\frac{\pi}{6}-\cos x\sin \frac{\pi}{6})$ Evaluate $\cos \frac{\pi}{3}$, $\sin \frac{\pi}{3}$, $\cos\frac{\pi}{6}$, and $\sin \frac{\pi}{6}$: $=(\cos x*\frac{1}{2}-\sin x*\frac{\sqrt{3}}{2})+(\sin x*\frac{\sqrt{3}}{2}-\cos x*\frac{1}{2})$ Simplify: $=\frac{1}{2}\cos x-\frac{\sqrt{3}}{2}\sin x+\frac{\sqrt{3}}{2}\sin x-\frac{1}{2}\cos x$ $=0$
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