Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 8: Techniques of Integration - Practice Exercises - Page 519: 92

Answer

$$\frac{2}{5}{y^{5/2}}{\left( {\ln y} \right)^2} - \frac{8}{{25}}{y^{5/2}}\ln y + \frac{{16}}{{125}}{y^{5/2}} + C$$

Work Step by Step

$$\eqalign{ & \int {{y^{3/2}}{{\left( {\ln y} \right)}^2}dy} \cr & {\text{Use the method of integration by parts}} \cr & \,\,\,\,\,\,\,\,\,{\text{Let }}\,\,\,\,\,u = {\left( {\ln y} \right)^2},\,\,\,\,\,du = \frac{{2\ln y}}{y}dy \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,dv = {y^{3/2}},\,\,\,\,\,v = \frac{2}{5}{y^{5/2}} \cr & \int {udv} = uv - \int {vdu} \,\,\,\, \cr & \to \,\,\,\int {{y^{3/2}}{{\left( {\ln y} \right)}^2}dy} = \frac{2}{5}{y^{5/2}}{\left( {\ln y} \right)^2} - \int {\left( {\frac{2}{5}{y^{5/2}}} \right)\left( {\frac{{2\ln y}}{y}} \right)} dy \cr & = \frac{2}{5}{y^{5/2}}{\left( {\ln y} \right)^2} - \int {\frac{4}{5}{y^{3/2}}\ln y} dy \cr & \cr & {\text{Use the method of integration by parts again}} \cr & \,\,\,\,\,\,\,\,\,{\text{Let }}\,\,\,\,\,u = \ln y,\,\,\,\,\,du = \frac{1}{y}dy \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,dv = \frac{4}{5}{y^{3/2}},\,\,\,\,\,v = \frac{8}{{25}}{y^{5/2}} \cr & = \frac{2}{5}{y^{5/2}}{\left( {\ln y} \right)^2} - \left( {\frac{8}{{25}}{y^{5/2}}\ln y - \int {\left( {\frac{8}{{25}}{y^{5/2}}} \right)\left( {\frac{1}{y}} \right)dy} } \right) \cr & = \frac{2}{5}{y^{5/2}}{\left( {\ln y} \right)^2} - \frac{8}{{25}}{y^{5/2}}\ln y + \frac{8}{{25}}\int {{y^{3/2}}dy} \cr & = \frac{2}{5}{y^{5/2}}{\left( {\ln y} \right)^2} - \frac{8}{{25}}{y^{5/2}}\ln y + \frac{8}{{25}}\left( {\frac{{{y^{5/2}}}}{{5/2}}} \right) + C \cr & = \frac{2}{5}{y^{5/2}}{\left( {\ln y} \right)^2} - \frac{8}{{25}}{y^{5/2}}\ln y + \frac{{16}}{{125}}{y^{5/2}} + C \cr} $$
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