Thomas' Calculus 13th Edition

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

Chapter 7: Transcendental Functions - Practice Exercises - Page 440: 62

Answer

$$2\left( {4{{\ln }^2}4 - {{\ln }^2}2} \right)=30(\ln{2})^2$$

Work Step by Step

$$\eqalign{ & \int_2^4 {\left( {1 + \ln t} \right)t\ln t} dt \cr & {\text{Use substitution:}}\cr &{\text{Let }}u = t\ln t,{\text{ so that }}du = \left( {1 + \ln t} \right)dt \cr & {\text{The new limits on }}u{\text{ are found as follows}} \cr & \,\,\,\,\,\,{\text{If }}t = 4,{\text{ then }}u = 4\ln 4 \cr & \,\,\,\,\,\,{\text{If }}t = 2,{\text{ then }}u = 2\ln 2 \cr & {\text{Then}} \cr & \int_2^4 {\left( {1 + \ln t} \right)t\ln t} dt = \int_{2\ln 2}^{4\ln 4} u du \cr & {\text{integrate}} \cr & = \left( {\frac{{{u^2}}}{2}} \right)_{2\ln 2}^{4\ln 4} \cr & {\text{use the fundamental theorem of calculus }}\int_a^b {f\left( x \right)} dx = F\left( b \right) - F\left( a \right).\,\,\,\,\left( {{\text{see page 281}}} \right) \cr & = \frac{{{{\left( {4\ln 4} \right)}^2}}}{2} - \frac{{{{\left( {2\ln 2} \right)}^2}}}{2} \cr & = \frac{1}{2}\left( {16{{\ln }^2}4 - 4{{\ln }^2}2} \right) \cr & = \frac{4}{2}\left( {4{{\ln }^2}4 - {{\ln }^2}2} \right) \cr & = 2\left( {4{{\ln }^2}4 - {{\ln }^2}2} \right) \cr} $$
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