Calculus: Early Transcendentals 8th Edition

Published by Cengage Learning
ISBN 10: 1285741552
ISBN 13: 978-1-28574-155-0

Chapter 4 - Section 4.4 - Indeterminate Forms and l''Hospital''s Rule - 4.4 Exercises - Page 312: 72

Answer

On the graph, we can see that both ratios have the same limit as $x \to 0$ $\lim\limits_{x \to 0}\frac{f(x)}{g(x)} = 4$

Work Step by Step

On the graph, we can see that both ratios have the same limit as $x \to 0$ $\lim\limits_{x \to 0}\frac{f(x)}{g(x)} = \lim\limits_{x \to 0}\frac{2x ~sin~x}{sec~x-1} = \frac{0}{0}$ We can apply L'Hospital's Rule twice. $\lim\limits_{x \to 0}\frac{f'(x)}{g'(x)} = \lim\limits_{x \to 0}\frac{2~sin~x+2x~cos~x}{sec~x~tan~x} = \frac{0}{0}$ $\lim\limits_{x \to 0}\frac{f''(x)}{g''(x)} = \lim\limits_{x \to 0}\frac{2~cos~x+2~cos~x-2x~sin~x}{sec~x~tan^2~x+sec^3~x} = \frac{2+2-0}{0+1} = 4$ Therefore: $\lim\limits_{x \to 0}\frac{f(x)}{g(x)} = 4$
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