Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 15 - Multiple Integrals - 15.1 Double Integrals over Rectangles - 15.1 Exercises - Page 1040: 21

Answer

$\frac{19ln2}{2} \approx 6.58$

Work Step by Step

$= \int_1^4 \int_1^2 (\frac{x}{y} + \frac{y}{x}) dy dx$ $= \int_1^4 (xlny + \frac{y^2}{2x})\big|_1^2 dx$ $= \int_1^4 [(xln2 + \frac{2}{x}) – (0 + \frac{1}{2x})] dx$ $= \int_1^4 (xln2 + \frac{2}{x} – \frac{1}{2x}) dx$ $= (\frac{x^2 ln2}{2} + 2lnx - \frac{lnx}{2})\big|_1^4$ $= [(8ln2 + 2ln4 - \frac{ln4}{2}) – (\frac{ln2}{2} + 0 - 0)]$ $= 8ln2 + 4ln2 – ln2 – \frac{ln2}{2}$ $= \frac{19ln2}{2}$ $\approx 6.58$
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