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: 3

Answer

\begin{aligned} x_{1}& \approx 2.166667 \\ x_{2}& \approx 2.154504 \\ x_{3}& \approx 2.154435 \end{aligned}

Work Step by Step

Given $$ f(x)=x^{3}-10, \quad x_{0}=2 $$ Since $$ x_{n+1}=x_{n}-\frac{f\left(x_{n}\right)}{f^{\prime}\left(x_{n}\right)}$$ Then \begin{align*} x_{n+1}&= x_n -\frac{x_n^{3}-10}{3x_n^2}\\ &=\frac{2 x^{3}+10}{3 x^{2} n} \end{align*} Hence \begin{aligned} x_{1}&=\frac{2 x_{0}^{3}+10}{3 x_{0}^{2}}= \frac{2 \cdot 2^{3}+10}{3 \cdot 2^{2}} \approx 2.166667 \\ x_{2}&=\frac{2 x_{1}^{3}+10}{3 x_{1}^{2}}=\frac{\frac{25}{4}+6}{5} \approx 2.154504 \\ x_{3}&=\frac{2 x_{2}^{3}+10}{3 x_{2}^{2}} =\frac{2(2.154504)^{3}+10}{3 (2.154504)^{2}} \approx 2.154435 \end{aligned}
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