Calculus with Applications (10th Edition)

Published by Pearson
ISBN 10: 0321749006
ISBN 13: 978-0-32174-900-0

Chapter 12 - Sequences and Series - 12.7 L'Hospital's Rule - 12.7 Exercises - Page 659: 8

Answer

$$ - 2$$

Work Step by Step

$$\eqalign{ & \mathop {\lim }\limits_{x \to 0} \frac{{{e^{2x}} - 1}}{{5{x^2} - x}} \cr & {\text{Verify if the conditions of l'Hospital's rule are satisfied}}{\text{. Here}} \cr & {\text{evaluate the limit substituting }}0{\text{ for }}x{\text{ into the numerator and }} \cr & {\text{denominator}}{\text{.}} \cr & \mathop {\lim }\limits_{x \to 0} \left( {{e^{2x}} - 1} \right) = {e^{2\left( 0 \right)}} - 1 = 0 \cr & \mathop {\lim }\limits_{x \to 0} \left( {5{x^2} - x} \right) = 5{\left( 0 \right)^2} - \left( 0 \right) = 0 \cr & \cr & {\text{Since the limits of both numerator and denominator are 0}}{\text{, }} \cr & {\text{l'Hospital's rule applies}}{\text{. Differentiating the numerator and}} \cr & {\text{denominator}}{\text{.}} \cr & {\text{for }}{e^{2x}} - 1 \to {D_x}\left( {{e^{2x}} - 1} \right) = 2{e^{2x}} \cr & {\text{for }}x \to {D_x}\left( {5{x^2} - x} \right) = 10x - 1 \cr & {\text{then}} \cr & \mathop {\lim }\limits_{x \to 0} \frac{{{e^{2x}} - 1}}{{5{x^2} - x}} = \mathop {\lim }\limits_{x \to 0} \frac{{2{e^{2x}}}}{{10x - 1}} \cr & {\text{Find the limit of the quotient of the derivatives}} \cr & = \frac{{2{e^{2\left( 0 \right)}}}}{{10\left( 0 \right) - 1}} \cr & = \frac{2}{{ - 1}} \cr & = - 2 \cr & {\text{By l'Hospital' rule}}{\text{, this result is the desired limit:}} \cr & \mathop {\lim }\limits_{x \to 0} \frac{{{e^{2x}} - 1}}{{5{x^2} - x}} = - 2 \cr} $$
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