University Calculus: Early Transcendentals (3rd Edition)

Published by Pearson
ISBN 10: 0321999584
ISBN 13: 978-0-32199-958-0

Chapter 2 - Additional and Advanced Exercises - Page 114: 30

Answer

$$\lim_{x\to9}\frac{\sin(\sqrt x-3)}{x-9}=\frac{1}{6}$$

Work Step by Step

$$A=\lim_{x\to9}\frac{\sin(\sqrt x-3)}{x-9}$$ $$A=\lim_{x\to9}\frac{\sin(\sqrt x-3)}{\sqrt x-3}\times\lim_{x\to9}\frac{\sqrt x-3}{x-9}$$ As $x\ne9$ then $\sqrt x-3\ne0$, and since $\lim_{x\to9}(\sqrt x-3)=\sqrt9-3=0$, we have $\lim_{x\to9}\frac{\sin(\sqrt x-3)}{\sqrt x-3}=1$. $$A=1\times\lim_{x\to9}\frac{\sqrt x-3}{x-9}$$ $$A=\lim_{x\to9}\frac{\sqrt x-3}{(\sqrt x)^2-3^2}$$ $$A=\lim_{x\to9}\frac{\sqrt x-3}{(\sqrt x-3)(\sqrt x+3)}$$ $$A=\lim_{x\to9}\frac{1}{\sqrt x+3}$$ $$A=\frac{1}{\sqrt9+3}=\frac{1}{6}$$
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