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: 14

Answer

The integral was evaluated as if the integrand is continuous on the interval. It is not, so the integral is improper, and diverges. Using a CAS, the result is "?" (undefined).

Work Step by Step

$\displaystyle \int_{-2}^{2}\frac{-2}{(x-1)^{3}}dx$ is an improper integral, because $\displaystyle \frac{-2}{(x-1)^{3}}$ is undefined at $x=1\in[-2,2].$ From the Definition of Improper Integrals with Infinite Discontinuities, 3. If $f$ is continuous on the interval $[a, b]$, except for some $c$ in $(a, b)$ at which $f$ has an infinite discontinuity, then $\displaystyle \int_{a}^{b}f(x)dx=\int_{a}^{c}f(x)dx+\int_{c}^{b}f(x)dx$ $\displaystyle =\lim_{c\rightarrow b^{-}}\int_{a}^{c}f(x)dx+\lim_{c\rightarrow a^{+}}\int_{c}^{b}f(x)dx$. $\displaystyle \int_{-2}^{2}\frac{1}{(x-1)^{3}}dx=\lim_{c\rightarrow 1^{-}}\int_{-2}^{c}-2(x-1)^{-3}dx+\lim_{c\rightarrow 1^{+}}\int_{c}^{2}-2(x-1)^{-3}dx$. $=\displaystyle \lim_{c\rightarrow 1^{-}}[\frac{1}{(x-1)^{2}}]_{-2}^{c}+\lim_{c\rightarrow 1^{+}}[\frac{1}{(x-1)^{2}}]_{c}^{2}$ $=(\displaystyle \infty-\frac{1}{9})+(1-\infty)$ Indefinite form $\infty-\infty$, the integral is undefined. The integral was evaluated as if the integrand is continuous on the interval. It is not, so the integral is improper, and diverges. Using a CAS, the result is "?" (undefined).
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