Calculus (3rd Edition)

Published by W. H. Freeman
ISBN 10: 1464125260
ISBN 13: 978-1-46412-526-3

Chapter 2 - Limits - 2.5 Evaluating Limits Algebraically - Exercises - Page 73: 42

Answer

$$ \lim _{x \rightarrow 27} \frac{x-27}{x^{1 / 3}-3}=27$$

Work Step by Step

Given $$ \lim _{x \rightarrow 27} \frac{x-27}{x^{1 / 3}-3}$$ let $$ f(x) = \frac{x-27}{x^{1 / 3}-3}$$ Since, we have $$ f( 27)= \frac{27-27}{3-3}=\frac{0}{0}$$ So, transform algebraically and cancel, we get \begin{aligned} L&= \lim _{x \rightarrow 27} \frac{x-27}{x^{1 / 3}-3}\\ &= \lim _{x \rightarrow 27} \frac{(x^\frac{1}{3})^3-3^3}{x^{1 / 3}-3}\\ &=\lim _{x \rightarrow 27} \frac{\left(x^{1 / 3}-3\right)\left(x^{2 / 3}+3 x^{1 / 3}+9\right)}{x^{1 / 3}-3}\\ &=\lim _{x \rightarrow 27}\left(x^{2 / 3}+3 x^{1 / 3}+9\right)\\ &=9+9+9\\ &=27 \end{aligned}
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