Calculus, 10th Edition (Anton)

Published by Wiley
ISBN 10: 0-47064-772-8
ISBN 13: 978-0-47064-772-1

Chapter 6 - Exponential, Logarithmic, And Inverse Trigonometric Functions - 6.2 Derivatives And Integrals Involving Logarithmic Functions - Exercises Set 6.2 - Page 426: 43

Answer

$$y = - \frac{x}{e}$$

Work Step by Step

$$\eqalign{ & {\text{Let }}f\left( x \right) = \ln \left( { - x} \right){\text{ and the point }}{x_0} = - e \cr & {\text{then }}f\left( {{x_0}} \right) = f\left( { - e} \right) = \ln \left( { - \left( { - e} \right)} \right) = 1 \cr & {\text{we have the point}}\left( { - e,1} \right) \cr & {\text{Find the derivative of }}f\left( x \right) \cr & f'\left( x \right) = \left( {\ln \left( { - x} \right)} \right)' \cr & f'\left( x \right) = \frac{{ - 1}}{{ - x}} \cr & f'\left( x \right) = \frac{1}{x} \cr & {\text{evaluate }}f'\left( x \right){\text{ at the point }}{x_0}{\text{ to find the slope}} \cr & f'\left( { - e} \right) = - \frac{1}{e} \cr & f'\left( { - e} \right) = - \frac{1}{e} \cr & {\text{then }}m = - \frac{1}{e} \cr & \cr & {\text{using the equation of the point - slope form }}y - {y_1} = m\left( {x - {x_1}} \right),{\text{ point }}\left( { - e,1} \right) \cr & y - \left( 1 \right) = - \frac{1}{e}\left( {x - \left( { - e} \right)} \right) \cr & {\text{Simplify}} \cr & y - 1 = - \frac{1}{e}\left( {x + e} \right) \cr & y - 1 = - \frac{x}{e} - 1 \cr & y = - \frac{x}{e} \cr} $$
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