Calculus with Applications (10th Edition)

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

Chapter 8 - Further Techniques and Applications of Integration - 8.4 Improper Integrals - 8.4 Exercises - Page 452: 34

Answer

$$ f(x)=\frac{3}{(x-1)^{3}} \text { for }(-\infty, 0] $$ the area between the graph of the given function and the x-axis over the given interval is given by: $$ \begin{split} \int_{-\infty}^{0} \frac{3}{(x-1)^{3}} d x &=-\frac{3}{2}. \end{split} $$ But, the area is positive, so the area between the graph of the given function and the x-axis over the given interval equal $\frac{3}{2}.$

Work Step by Step

$$ f(x)=\frac{3}{(x-1)^{3}} \text { for }(-\infty, 0] $$ the area between the graph of the given function and the x-axis over the given interval is given by: $$ \begin{split} \int_{-\infty}^{0} \frac{3}{(x-1)^{3}} d x &=\lim _{a \rightarrow-\infty} \int_{a}^{0} \frac{3}{(x-1)^{3}} d x \\ &=\left.\lim _{a \rightarrow-\infty}\left(\frac{3(x-1)^{-2}}{-2}\right)\right|_{a} ^{0} \\ &=\left.\lim _{a \rightarrow-\infty}\left(-\frac{3}{2(x-1)^{2}}\right)\right|_{a} ^{0}\\ &=\lim _{a \rightarrow-\infty}\left(-\frac{3}{2}+\frac{3}{2(a-1)^{2}}\right)\\ &=-\frac{3}{2}+\lim _{a \rightarrow-\infty}\left(\frac{3}{2(a-1)^{2}}\right)\\ &=-\frac{3}{2}+0\\ &=-\frac{3}{2}. \end{split} $$ Thus the given improper integral $$ \int_{-\infty}^{0} \frac{3}{(x-1)^{3}} d x=-\frac{3}{2}. $$ But, the area is positive, so the area between the graph of the given function and the x-axis over the given interval equal $\frac{3}{2}.$
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