Calculus: Early Transcendentals (2nd Edition)

Published by Pearson
ISBN 10: 0321947347
ISBN 13: 978-0-32194-734-5

Chapter 3 - Derivatives - Review Exercises - Page 234: 55

Answer

$$\frac{3}{4}\pi $$

Work Step by Step

$$\eqalign{ & {\text{Let the limit }}\mathop {\lim }\limits_{x \to 5} \frac{{\tan \left( {\pi \sqrt {3x - 11} } \right)}}{{x - 5}} \cr & {\text{Rewrite the expression}} \cr & \mathop {\lim }\limits_{x \to 5} \frac{{\tan \left( {\pi \sqrt {3x - 11} } \right)}}{{x - 5}} = \mathop {\lim }\limits_{x \to 5} \frac{{\tan \left( {\pi \sqrt {3x - 11} } \right) - \overbrace {\tan \left( {\pi \sqrt {3\left( 5 \right) - 11} } \right)}^{{\text{equal to 0}}}}}{{x - 5}} \cr & = \mathop {\lim }\limits_{x \to 5} \frac{{\tan \left( {\pi \sqrt {3x - 11} } \right) - \tan \left( {2\pi } \right)}}{{x - 5}} \cr & {\text{using the definition of the derivative }}f'\left( a \right) = \mathop {\lim }\limits_{x \to a} \frac{{f\left( x \right) - f\left( a \right)}}{{x - a}} \cr & \underbrace {\mathop {\lim }\limits_{x \to 5} \frac{{\tan \left( {\pi \sqrt {3x - 11} } \right) - \tan \left( {2\pi } \right)}}{{x - 5}}}_{\mathop {\lim }\limits_{x \to a} \frac{{f\left( x \right) - f\left( a \right)}}{{x - a}}} \cr & \Rightarrow f\left( x \right) = \tan \left( {\pi \sqrt {3x - 11} } \right){\text{ }}and{\text{ }}a = 5 \cr & {\text{With the definition of derivative:}} \cr & f'\left( x \right) = \frac{d}{{dx}}\left[ {\tan \left( {\pi \sqrt {3x - 11} } \right)} \right] \cr & f'\left( x \right) = {\sec ^2}\left( {\pi \sqrt {3x - 11} } \right)\frac{d}{{dx}}\left[ {\pi \sqrt {3x - 11} } \right] \cr & f'\left( x \right) = \pi {\sec ^2}\left( {\pi \sqrt {3x - 11} } \right)\left( {\frac{3}{{2\sqrt {3x - 11} }}} \right) \cr & {\text{At }}x = 5 \cr & f'\left( 5 \right) = \pi {\sec ^2}\left( {\pi \sqrt {3\left( 5 \right) - 11} } \right)\left( {\frac{3}{{2\sqrt {3\left( 5 \right) - 11} }}} \right) \cr & f'\left( 5 \right) = \pi {\sec ^2}\left( {2\pi } \right)\left( {\frac{3}{4}} \right) \cr & f'\left( 5 \right) = \pi \left( 1 \right)\left( {\frac{3}{4}} \right) \cr & f'\left( 5 \right) = \frac{3}{4}\pi \cr & {\text{Therefore}}{\text{,}} \cr & \mathop {\lim }\limits_{x \to 5} \frac{{\tan \left( {\pi \sqrt {3x - 11} } \right)}}{{x - 5}} = \frac{3}{4}\pi \cr} $$
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