Calculus: Early Transcendentals 8th Edition

Published by Cengage Learning
ISBN 10: 1285741552
ISBN 13: 978-1-28574-155-0

Chapter 7 - Review - Exercises - Page 538: 47

Answer

The given improper integral is: $$ \int_{0}^{1} \frac{x-1}{\sqrt{x}} dx = -\frac{4}{3} $$

Work Step by Step

$$ \int_{0}^{1} \frac{x-1}{\sqrt{x}} dx $$ Observe that the given integral is improper because $ f(x)=\frac{x-1}{\sqrt{x}} $ has the vertical asymptote $x =0 $. Since the infinite discontinuity occurs at the left endpoint of $ [0, 1] $ , we must use part (b) of Definition 3 : $$ \begin{aligned} \int_{0}^{1} \frac{x-1}{\sqrt{x}} d x &= \lim _{t \rightarrow 0^{+}} \int_{t}^{1}\left(\frac{x}{\sqrt{x}}-\frac{1}{\sqrt{x}}\right) d x =\lim _{t \rightarrow 0^{+}} \int_{t}^{1}\left(x^{1 / 2}-x^{-1 / 2}\right) d x=\lim _{t \rightarrow 0^{+}}\left[\frac{2}{3} x^{3 / 2}-2 x^{1 / 2}\right]_{t}^{1} \\ &=\lim _{t \rightarrow 0^{+}}\left[\left(\frac{2}{3}-2\right)-\left(\frac{2}{3} t^{3 / 2}-2 t^{1 / 2}\right)\right]=-\frac{4}{3}-0=-\frac{4}{3} \end{aligned} $$ \begin{aligned} \int_{0}^{1} \frac{x-1}{\sqrt{x}} d x &=\lim _{t \rightarrow 0^{+}} \int_{t}^{1}\left(\frac{x}{\sqrt{x}}-\frac{1}{\sqrt{x}}\right) d x \\ &=\lim _{t \rightarrow 0^{+}} \int_{t}^{1}\left(x^{1 / 2}-x^{-1 / 2}\right) d x \\ &= \lim _{t \rightarrow 0^{+}}\left[\frac{2}{3} x^{3 / 2}-2 x^{1 / 2}\right]_{t}^{1} \\ &= \lim _{t \rightarrow 0^{+}}\left[\left(\frac{2}{3}-2\right)-\left(\frac{2}{3} t^{3 / 2}-2 t^{1 / 2}\right)\right]\\ &= -\frac{4}{3}-0=-\frac{4}{3} \end{aligned} Thus, the given improper integral is: $$ \int_{0}^{1} \frac{x-1}{\sqrt{x}} dx = -\frac{4}{3} $$
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