Calculus with Applications (10th Edition)

Published by Pearson
ISBN 10: 0321749006
ISBN 13: 978-0-32174-900-0

Chapter 7 - Integration - 7.6 Numerical Integration - 7.6 Exercises - Page 413: 3

Answer

$$ \int_{-1}^{3} \frac{3}{5-x} d x $$ Here $a=-1, b=3,$ and $n=4,$ with $(b-a) / n=(3+1) / 4=1 $ as the altitude of each trapezoid. Then $x_{0}=-1, x_{1}=0, x_{2}=1, x_{3}=2,$ and $x_{4}=3 .$ Now find the corresponding function values. The work can be organized into a table, as follows. $$ \begin{aligned} &n=4, b=3, a=-1, f(x)=\frac{3}{5-x}\\ &\begin{array}{c|c|l} \hline i & x_{i} & f\left(x_{i}\right) \\ \hline 0 & -1 & 0.5 \\ 1 & 0 & 0.6 \\ 2 & 1 & 0.75 \\ 3 & 2 & 1 \\ 4 & 3 & 1.5 \\ \hline \end{array} \end{aligned} $$ (a) the trapezoidal rule: $$ \begin{array}{l} \int_{-1}^{3} \frac{3}{5-x} d x \\ \quad \approx \frac{3-(-1)}{4}\left[\frac{1}{2}(0.5)+0.6+0.75+1+\frac{1}{2}(1.5)\right] \\ \quad=1(3.35) \\ \quad=3.35 \end{array} $$ (b) Simpson’s Rule: $$ \begin{array}{l} \int_{-1}^{3} \frac{3}{5-x} d x \\ \quad \approx \frac{3-(-1)}{3(4)}[0.5+4(0.6)+2(0.75)+4(1)+1.5] \\ \quad=\frac{1}{3}\left(\frac{99}{10}\right) \\ \quad=\frac{33}{10} \approx 3.3 \end{array} $$ (c) Exact value: $$ \begin{aligned} \int_{-1}^{3} \frac{3}{5-x} d x &=-\left.3 \ln |5-x|\right|_{-1} ^{3} \\ &=-3(\ln |2|-\ln |6|) \\ &=3 \ln 3 \approx 3.296 \end{aligned} $$

Work Step by Step

$$ \int_{-1}^{3} \frac{3}{5-x} d x $$ Here $a=-1, b=3,$ and $n=4,$ with $(b-a) / n=(3+1) / 4=1 $ as the altitude of each trapezoid. Then $x_{0}=-1, x_{1}=0, x_{2}=1, x_{3}=2,$ and $x_{4}=3 .$ Now find the corresponding function values. The work can be organized into a table, as follows. $$ \begin{aligned} &n=4, b=3, a=-1, f(x)=\frac{3}{5-x}\\ &\begin{array}{c|c|l} \hline i & x_{i} & f\left(x_{i}\right) \\ \hline 0 & -1 & 0.5 \\ 1 & 0 & 0.6 \\ 2 & 1 & 0.75 \\ 3 & 2 & 1 \\ 4 & 3 & 1.5 \\ \hline \end{array} \end{aligned} $$ (a) the trapezoidal rule: $$ \begin{array}{l} \int_{-1}^{3} \frac{3}{5-x} d x \\ \quad \approx \frac{3-(-1)}{4}\left[\frac{1}{2}(0.5)+0.6+0.75+1+\frac{1}{2}(1.5)\right] \\ \quad=1(3.35) \\ \quad=3.35 \end{array} $$ (b) Simpson’s Rule: $$ \begin{array}{l} \int_{-1}^{3} \frac{3}{5-x} d x \\ \quad \approx \frac{3-(-1)}{3(4)}[0.5+4(0.6)+2(0.75)+4(1)+1.5] \\ \quad=\frac{1}{3}\left(\frac{99}{10}\right) \\ \quad=\frac{33}{10} \approx 3.3 \end{array} $$ (c) Exact value: $$ \begin{aligned} \int_{-1}^{3} \frac{3}{5-x} d x &=-\left.3 \ln |5-x|\right|_{-1} ^{3} \\ &=-3(\ln |2|-\ln |6|) \\ &=3 \ln 3 \approx 3.296 \end{aligned} $$
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