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: 38

Answer

$$\lim _{x \rightarrow 3} \frac{x^{3}-27}{x^{2}-9}= \frac{9 }{2} $$

Work Step by Step

Given $$\lim _{x \rightarrow 3} \frac{x^{3}-27}{x^{2}-9}$$ let $$ f(x) = \lim _{x \rightarrow 3} \frac{x^{3}-27}{x^{2}-9}$$ Since, we have $$ f( 3)= \lim _{x \rightarrow 3} \frac{27-27}{9-9}=\frac{0}{0}$$ So, transform algebraically and cancel, we get \begin{aligned} L&=\lim _{x \rightarrow 3} \frac{x^{3}-27}{x^{2}-9}\\ &= \lim _{x \rightarrow 3} \frac{(x-3)(x^2+3x+9)}{(x-3)(x+3)}\\ &= \lim _{x \rightarrow 3} \frac{ (x^2+3x+9)}{ (x+3)}\\ &= \frac{9+9+9 }{3+3}\\ &= \frac{27 }{6} \\ &=\frac{9 }{2} \end{aligned}
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