Calculus: Early Transcendentals 9th Edition

Published by Cengage Learning
ISBN 10: 1337613924
ISBN 13: 978-1-33761-392-7

Chapter 4 - Section 4.8 - Newton''s Method - 4.8 Exercises - Page 355: 20

Answer

$x = 0.653060$

Work Step by Step

$$\eqalign{ & \ln x = \frac{1}{{x - 3}} \cr & {\text{Let }}y = \ln x,{\text{ }}y = \frac{1}{{x - 3}} \cr & {\text{The graphs of the functions are shown below}} \cr & \cr & {\text{Find the intersection points}}{\text{, let }}y = y \cr & \ln x = \frac{1}{{x - 3}} \cr & {\text{Subtract }}x - 1{\text{ from both sides of equation to write the functions}} \cr & {\text{in the form }}f\left( x \right) = g\left( x \right) - h\left( x \right) = 0 \cr & f\left( x \right) = 0 \cr & \ln x - \frac{1}{{x - 3}} = 0 \cr & \cr & {\text{Let }}f\left( x \right) = \ln x - \frac{1}{{x - 3}},{\text{ and differentiate}} \cr & f'\left( x \right) = \frac{d}{{dx}}\left[ {\ln x - \frac{1}{{x - 3}}} \right] \cr & f'\left( x \right) = \frac{1}{x} + \frac{1}{{{{\left( {x - 3} \right)}^2}}} \cr & {\text{Use the procedure Newton's Method for Approximations}} \cr & {\text{Roots of }}f\left( x \right) = 0{\text{ }}\left( {{\text{See page 352}}} \right) \cr & {x_{n + 1}} = {x_n} - \frac{{f\left( {{x_n}} \right)}}{{f'\left( {{x_n}} \right)}} \cr & {\text{Substituting }}f\left( {{x_n}} \right){\text{ and }}f'\left( {{x_n}} \right){\text{ the Newton's method takes the}} \cr & {\text{form}} \cr & {x_{n + 1}} = {x_n} - \frac{{\ln {x_n} - \frac{1}{{{x_n} - 3}}}}{{\frac{1}{{{x_n}}} + \frac{1}{{{{\left( {{x_n} - 3} \right)}^2}}}}} \cr & {\text{From the graph we can see that the first possible initial }} \cr & {\text{approximation is }}{x_1} = 0.6 \cr & {\text{If we choose }}{x_1} = 2{\text{ as the initial approximation}},{\text{then we obtain}} \cr & {x_2} = 0.6 - \frac{{\ln \left( {0.6} \right) - \frac{1}{{0.6 - 3}}}}{{\frac{1}{{0.6}} + \frac{1}{{{{\left( {0.6 - 3} \right)}^2}}}}} \cr & {x_2} \approx 0.651166 \cr & {x_3} \approx 0.653057 \cr & {x_4} \approx 0.653060 \cr & {x_5} \approx 0.653060 \cr & {x_4}{\text{ and }}{x_5}{\text{ are agree to six decimal places}}{\text{, we conclude that}} \cr & {\text{the solution of the equation }}\ln x = \frac{1}{{x - 3}}{\text{ is}} \cr & x = 0.653060 \cr} $$
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