Calculus: Early Transcendentals 9th Edition

Published by Cengage Learning
ISBN 10: 1337613924
ISBN 13: 978-1-33761-392-7

Chapter 2 - Section 2.3 - Calculating Limits Using the Limit Laws - 2.3 Exercises - Page 103: 18

Answer

$\frac{{11}}{{10}}$

Work Step by Step

$$\eqalign{ & \mathop {\lim }\limits_{x \to - 5} \frac{{2{x^2} + 9x - 5}}{{{x^2} - 25}} \cr & {\text{Evaluate the limit by using the Direct Substitution Property}} \cr & \mathop {\lim }\limits_{x \to a} f\left( x \right) = f\left( a \right) \cr & \cr & {\text{Therefore}}{\text{,}} \cr & \mathop {\lim }\limits_{x \to - 5} \frac{{2{x^2} + 9x - 5}}{{{x^2} - 25}} = \frac{{2{{\left( { - 5} \right)}^2} + 9\left( { - 5} \right) - 5}}{{{{\left( { - 5} \right)}^2} - 25}} \cr & \cr & {\text{Simplifying}} \cr & \mathop {\lim }\limits_{x \to - 5} \frac{{2{x^2} + 9x - 5}}{{{x^2} - 25}} = \frac{{50 - 45 - 5}}{{25 - 25}} = \frac{0}{0}{\text{ Indeterminate}} \cr & \cr & {\text{Factoring the numerator and denominator}} \cr & \mathop {\lim }\limits_{x \to - 5} \frac{{2{x^2} + 9x - 5}}{{{x^2} - 25}} = \mathop {\lim }\limits_{x \to - 5} \frac{{\left( {2x - 1} \right)\left( {x + 5} \right)}}{{\left( {x + 5} \right)\left( {x - 5} \right)}} \cr & {\text{Cancel the common factor }}x + 5 \cr & = \mathop {\lim }\limits_{x \to - 5} \frac{{2x - 1}}{{x - 5}} \cr & \cr & {\text{Evaluate the limit}} \cr & \mathop {\lim }\limits_{x \to - 5} \frac{{2x - 1}}{{x - 5}} = \frac{{2\left( { - 5} \right) - 1}}{{ - 5 - 5}} = \frac{{ - 10 - 1}}{{ - 10}} = \frac{{11}}{{10}} \cr & {\text{Then}} \cr & \mathop {\lim }\limits_{x \to - 5} \frac{{2{x^2} + 9x - 5}}{{{x^2} - 25}} = \frac{{11}}{{10}} \cr} $$
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