Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 2 - Derivatives - 2.4 Derivatives of Trigonometric Functions - 2.4 Exercises - Page 150: 25

Answer

$y=2x$

Work Step by Step

Given $$y= 2x \sin x\ \ \ \ \ \ (\pi/2,\pi )$$ Since \begin{aligned} y'&= 2\left(\frac{d}{dx}\left(x\right)\sin \left(x\right)+\frac{d}{dx}\left(\sin \left(x\right)\right)x\right)\\ &= 2\left(\sin \left(x\right)+x\cos \left(x\right)\right) \end{aligned} Then \begin{aligned} m&= y'\bigg|_{(\pi/2,\pi)}\\ &= 2[\sin(\pi/2)+ \frac{\pi}{2} \cos(\pi/2)]\\ &= 2 \end{aligned} Hence the tangent line equation given by \begin{aligned} \frac{y-y_1}{x-x_1}&=m\\ \frac{y-\pi}{x-\frac{\pi}{2}}&= 2\\ y-\pi &= 2x-\pi\\ y&= 2x \end{aligned}
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