Calculus 8th Edition

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

Chapter 10 - Parametric Equations and Polar Coordinates - 10.3 Polar Coordinates - 10.3 - Page 707: 57

Answer

$TLS\vert_{{\pi}}=-\pi$

Work Step by Step

Given: $r=\frac{1}{{{\pi}}}$ $\theta={\pi}$ Use the equation for tangent line slope for polar coordinates: $TLS=\frac{\frac{dr}{d\theta}sin\theta+rcos\theta}{\frac{dr}{d\theta}cos\theta-rsin\theta}$ Find $\frac{dr}{d\theta}$: $\frac{dr}{d\theta}=(\frac{1}{{{\pi}}})^{\prime}={-\frac{1}{{{\pi}}^2}}$ Plug in for $r$, $\theta$, and $\frac{dr}{d\theta}$: $TLS\vert_{\pi}=\frac{(-\frac{1}{{{\pi}}^2})sin({\pi})+(\frac{1}{{{\pi}}})cos({\pi})}{({-\frac{1}{{{\pi}}^2}})cos({\pi})-(\frac{1}{{{\pi}}})sin({\pi})}=\frac{(-\frac{1}{{{\pi}}^2})sin({\pi})+(\frac{1}{{{\pi}}})cos({\pi})}{({-\frac{1}{{{\pi}}^2}})cos({\pi})-(\frac{1}{{{\pi}}})sin({\pi})}$ Solve: $sin({\pi})=0$ $cos({\pi})=-1$ Simplify: $TLS\vert_{{\pi}}=\frac{(-\frac{1}{{{\pi}}^2})(0)+(\frac{1}{{{\pi}}})(1)}{({-\frac{1}{{{\pi}}^2}})(1)-(\frac{1}{{{\pi}}})(0)}=\frac{\frac{1}{\pi}}{-\frac{1}{\pi^2}}=\frac{1}{\pi}*-\frac{\pi^2}{1}=-\pi$
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