Calculus 10th Edition

Published by Brooks Cole
ISBN 10: 1-28505-709-0
ISBN 13: 978-1-28505-709-5

Chapter 8 - Integration Techniques, L'Hopital's Rule, and Improper Integrals - 8.8 Exercises - Page 575: 38

Answer

$$0$$

Work Step by Step

$$\eqalign{ & \int_0^e {\ln {x^2}} dx \cr & {\text{Use logarithmic properties}} \cr & = \int_0^e {2\ln x} dx \cr & = 2\int_0^e {\ln x} dx \cr & \ln x{\text{ is not defined at }}x = 0,{\text{so we can write}} \cr & 2\int_0^e {\ln x} dx = 2\mathop {\lim }\limits_{b \to {0^ + }} \int_b^e {\ln x} dx \cr & {\text{Integrate }}\int {\ln x} dx{\text{ by parts}} \cr & u = \ln x,{\text{ }}du = \frac{1}{x}dx,{\text{ }}dv = dx,{\text{ }}v = x \cr & \int {udv} = uv - \int {vdu} = x\ln x - \int {x\left( {\frac{1}{x}} \right)dx} \cr & = x\ln x - x + C \cr & \cr & 2\mathop {\lim }\limits_{b \to {0^ + }} \int_b^e {\ln x} dx = \mathop {\lim }\limits_{b \to {0^ + }} \left[ {x\ln x - x} \right]_b^e \cr & = 2\mathop {\lim }\limits_{b \to {0^ + }} \left[ {e\ln e - e} \right] - 2\mathop {\lim }\limits_{b \to {0^ + }} \left[ {b\ln b - b} \right] \cr & = 2\mathop {\lim }\limits_{b \to {0^ + }} \left( 0 \right) - 2\mathop {\lim }\limits_{b \to {0^ + }} \left[ {b\ln b - b} \right] \cr & {\text{Evaluate the limit when }}b \to {0^ + } \cr & = - 2\left( 0 \right) - 2\left[ {0 - \left( 0 \right)} \right] \cr & = 0 \cr & {\text{The following graph confirms the result}} \cr} $$
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