Calculus (3rd Edition)

Published by W. H. Freeman
ISBN 10: 1464125260
ISBN 13: 978-1-46412-526-3

Chapter 4 - Applications of the Derivative - 4.7 Newton's Method - Exercises - Page 219: 6

Answer

\begin{aligned} &x_{1} \approx 6.393542\\ &x_{2} \approx 6.439307\\ &x_{3} \approx 6.439117 \end{aligned}

Work Step by Step

Given $$f(x)=1-x \sin x, \quad x_{0}=7$$ Since $$ x_{n+1}=x_{n}-\frac{f\left(x_{n}\right)}{f^{\prime}\left(x_{n}\right)}$$ Then \begin{aligned} x_{n+1} &=x_{n}-\frac{1-x_{n} \sin x_{n}}{-\sin x_{n}-x_{n} \cos x_{n}} \\ &=\frac{x_{n} \sin x_{n}+x_{n}^{2} \cos x_{n}+1-x_{n} \sin x_{n}}{\sin x_{n}+x_{n} \cos x_{n}} \\ &=\frac{x_{n}^{2} \cos x_{n}+1}{\sin x_{n}+x_{n} \cos x_{n}} \end{aligned} Hence \begin{aligned} &x_{1}=\frac{x_{0}^{2} \cos x_{0}+1}{\sin x_{0}+x_{0} \cos x_{0}}= \frac{(7)^{2} \cos (7)+1}{\sin (7)+(7) \cos (7)} \approx 6.393542\\ &x_{2}=\frac{x_{1}^{2} \cos x_{1}+1}{\sin x_{1}+x_{1} \cos x_{1}}= \frac{( 6.393)^{2} \cos ( 6.393)+1}{\sin ( 6.393)+( 6.393) \cos ( 6.393)} \approx 6.439307\\ &x_{3}=\frac{x_{2}^{2} \cos x_{2}+1}{\sin x_{2}+x_{2} \cos x_{2}} = \frac{( 6.439)^{2} \cos ( 6.439)+1}{\sin ( 6.439)+( 6.439) \cos ( 6.439)}\approx 6.439117 \end{aligned}
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