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Write the Derivative of F (X) = |X|3 at X = 0. - Mathematics

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Question

Write the derivative of f (x) = |x|3 at x = 0.

Answer in Brief
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Solution

Given:  

 
`f(x) = |x|^3 = {(x^3, xge0),(-x^3 , x<0):}`

(LHD at = 0)

\[\lim_{x \to 0^-} \frac{f(x) - f(0)}{x - 0}\]
\[ = \lim_{h \to 0} \frac{f(0 - h) - f(0)}{x}\]
\[ = \lim_{h \to 0} \frac{h^3}{- h} \]
\[ = 0\]

(RHD at x = 0)

\[\lim_{x \to 0^+} \frac{f(x) - f(0)}{x - 0} \]
\[ = \lim_{x \to 0^+} \frac{f(0 + h) - f(0)}{x}\]
\[ = \lim_{h \to 0} \frac{h^3 - 0}{h} \]
\[ = 0\]

and 

\[f(0) = 0 .\]

Thus, (LHD at x=0) = (RHD at x = 0) = 

\[f(0)\]

Hence, 

\[\lim_{x \to 0} \frac{f(x) - f(0)}{x - 0} = f'(0) = 0\]
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Chapter 10: Differentiability - Exercise 10.3 [Page 17]

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RD Sharma Mathematics [English] Class 12
Chapter 10 Differentiability
Exercise 10.3 | Q 9 | Page 17

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