Calculus with Applications (10th Edition)

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

Chapter 9 - Multiveriable Calculus - 9.6 Double Integrals - 9.6 Exercises - Page 514: 44

Answer

$$4\ln 4 - 3$$

Work Step by Step

$$\eqalign{ & \int_1^4 {\int_x^{{x^2}} {\frac{1}{y}} dydx} \cr & = \int_1^4 {\left[ {\int_x^{{x^2}} {\frac{1}{y}} dy} \right]dx} \cr & {\text{solve the inner integral by treating }}x{\text{ as a constant}} \cr & = \int_x^{{x^2}} {\frac{1}{y}} dy \cr & {\text{integrate}} \cr & = \left[ {\ln \left| y \right|} \right]_x^{{x^2}} \cr & {\text{evaluating the limits}} \cr & = \ln \left| {{x^2}} \right| - \ln \left| x \right| \cr & {\text{simplifying by using logarithmic properties}} \cr & = \ln \left( {\frac{{{x^2}}}{x}} \right) \cr & = \ln x \cr & \cr & \int_1^4 {\left[ {\int_x^{{x^2}} {\frac{1}{y}} dy} \right]dx} = \int_1^4 {\ln xdx} \cr & {\text{integrating by parts }}\int u dv = uv - \int {vdu} \cr & \,\,\,\,\,u = \ln x,\,\,\,du = \frac{1}{x}dx,\,\,\,\,\,dv = dx,\,\,\,\,\,\,v = x \cr & \,\,\,\,\int {\ln x} dx = x\ln x - \int {x\left( {\frac{1}{x}} \right)} dx \cr & \,\,\,\,\,\,\, = x\ln x - \int {dx} \cr & \,\,\,\,\, = x\ln x - x + C \cr & {\text{then}} \cr & \int_1^4 {\ln xdx} = \left( {x\ln x - x} \right)_1^4 \cr & {\text{evaluate}} \cr & = \left( {4\ln 4 - 4} \right) - \left( {\ln 1 - 1} \right) \cr & {\text{simplifying}} \cr & = 4\ln 4 - 4 + 1 \cr & = 4\ln 4 - 3 \cr} $$
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