Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 1 - Functions and Limits - Principles of Problem Solving - Problems - Page 103: 15

Answer

$$ \lim _{x \rightarrow 1} \frac{\sqrt[3]{x}-1}{\sqrt{x}-1}=\frac{2}{3} $$

Work Step by Step

$$ \lim _{x \rightarrow 1} \frac{\sqrt[3]{x}-1}{\sqrt{x}-1} $$ Let $t=\sqrt[6]{x},$ so $x=t^{6} .$ Then $t \rightarrow 1$ as $x \rightarrow 1,$ so $$ \begin{aligned} \lim _{x \rightarrow 1} \frac{\sqrt[3]{x}-1}{\sqrt{x}-1}&=\lim _{t \rightarrow 1} \frac{t^{2}-1}{t^{3}-1} \\ &=\lim _{t \rightarrow 1} \frac{(t-1)(t+1)}{(t-1)\left(t^{2}+t+1\right)}\\ &=\lim _{t \rightarrow 1} \frac{t+1}{t^{2}+t+1}\\ &=\frac{1+1}{1^{2}+1+1}\\ &=\frac{2}{3} \end{aligned} $$
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