Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 2 - Derivatives - Problems Plus - Problems - Page 202: 20

Answer

Proof

Work Step by Step

We know that definition of derivative \[F'(c)=\lim_{x\rightarrow c}\frac{F(x)-F(c)}{x-c}\;\;\;...(1)\] It is given that $f $ and $g$ are differentiable function \[f'(0)=\lim_{x\rightarrow 0}\frac{f(x)-f(0)}{x-0}\] Also it is given that $f(0)=0$ \[f'(0)=\lim_{x\rightarrow 0}\frac{f(x)}{x}\;\;\;...(2)\] Similarly, \[g'(0)=\lim_{x\rightarrow 0}\frac{g(x)-g(0)}{x-0}\] Also it is given that $g(0)=0$ \[g'(0)=\lim_{x\rightarrow 0}\frac{g(x)}{x}\;\;\;...(3)\] Using (2) and (3) \[\Rightarrow \frac{f'(0)}{g'(0)}=\frac{\lim_{x\rightarrow 0}\frac{f(x)}{x}}{\lim_{x\rightarrow 0}\frac{g(x)}{x}}\] \[\Rightarrow \frac{f'(0)}{g'(0)}=\lim_{x\rightarrow 0}\frac{\frac{f(x)}{x}}{\frac{g(x)}{x}}\] \[\Rightarrow \frac{f'(0)}{g'(0)}=\lim_{x\rightarrow 0}\frac{f(x)}{g(x)}\] Hence proven.
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