Calculus 10th Edition

Published by Brooks Cole
ISBN 10: 1-28505-709-0
ISBN 13: 978-1-28505-709-5

Chapter 1 - Limits and Their Properties - 1.3 Exercises - Page 68: 82

Answer

Please see below. $$\begin{array}{|c|c|c|c|c|c|c|c|} \hline x & -0.1 & -0.01 & - 0.001 & 0 & 0.001 & 0.01 & 0.1 \\ \hline \frac{\sin x}{\sqrt[3]{x}} & 0.21508458 & 0.046415115 & 0.0099999983 & \text{undefined} & 0.0099999983 & 0.046415115 & 0.21508458 \\ \hline \end{array}$$

Work Step by Step

Looking at the graph, we find that when $x$ approaches $0$ from the left and right, the function approaches $0$. So, we can conclude that$$\lim_{x \to 0}\frac{\sin x}{\sqrt[3]{x}}=0 \, .$$ The table confirms our result. Now, we find the limit analytically. Since by direct substitution we get the indeterminate form $\frac{0}{0}$, we multiply the numerator and denominator by $\sqrt[3]{x^2}$ (We can do this since $x \neq 0$). So, we have$$\lim_{x \to 0}\frac{\sin x}{\sqrt[3]{x}}=\lim_{x \to 0}\left ( \vphantom{\frac{\sin x^2}{x^2}} \sqrt[3]{x^2} \right ) \left (\frac{\sin x}{x} \right )= (0)(1)=0$$(In finding the limit we have used Thereom 1.9 (a), $\lim_{x \to 0} \frac{\sin x}{x}=1$).
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