Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 3: Derivatives - Section 3.1 - Tangents and the Derivative at a Point - Exercises 3.1 - Page 109: 36

Answer

The graph of $g(x)$ does not have a tangent at the origin.

Work Step by Step

We have $g'(0)=\lim\limits_{h\to0}\dfrac{g(h+0)-g(0)}{h}=\lim\limits_{h\to0}\dfrac{g(h)-g(0)}{h}$ As we know that when $h\to0$, $h\ne 0$ , thus $g(h)=h\sin(\dfrac{1}{h})$ and $g'(0)=\lim\limits_{h\to0}\dfrac{h\sin(\dfrac{1}{h})-0}{h}=\lim\limits_{h\to0}\dfrac{h\sin(\dfrac{1}{h})}{h}$ $\implies g'(0)=\lim\limits_{h\to0}\sin(\dfrac{1}{h})$ As $h\to0$, then $\lim\limits_{h\to0} \sin(\dfrac{1}{h})$ does not exist, because the graph of $\sin(\dfrac{1}{h})$ will be oscillating at high peak to get a definite value. Hence, the graph of $g(x)$ does not have a tangent at the origin.
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