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Write the Points Where F (X) = |Loge X| is Not Differentiable. - Mathematics

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Question

Write the points where f (x) = |loge x| is not differentiable.

Answer in Brief
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Solution

Given:  

`f(x) |log_e x| = {(-log_e,x, ,0 <x<1,),(log_e,x, ,x≥1,):}`

Clearly 

\[f(x)\]  is differentiable for all 
\[x > 1\]  and for all 
\[x < 1\] . So, we have to check the differentiability at 
\[x = 1\]
We have,
(LHD at x = 1) 
\[\lim_{x \to 1^-} \frac{f(x) - f(1)}{x - 1} \]
\[= \lim_{x \to 1^-} \frac{- \log x - \log 1}{x - 1}\]
\[ = - \lim_{x \to 1^-} \frac{\log x}{x - 1}\]
\[ = - \lim_{h \to 0} \frac{\log (1 - h)}{1 - h - 1}\]
\[ = - \lim_{h \to 0} \frac{\log (1 - h)}{- h} \]
\[ = - 1\]

(RHD at x=1)

\[\lim_{x \to 1^+} \frac{f(x) - f(1)}{x - 1}\]

\[= \lim_{x \to 1^+} \frac{\log x - \log 1}{x - 1}\]
\[ = \lim_{x \to 1^+} \frac{\log x}{x - 1}\]
\[ {= \lim_{h \to 0}}_{} \frac{\log (1 + h)}{1 + h - 1}\]
\[ = \lim_{h \to 0} \frac{\log (1 + h)}{h}\]
\[ = 1\]

Thus, (LHD at x =1) ≠ (RHD at x =1)
So, 

\[f(x)\]  is not differentiable at 
\[x = 1 .\]
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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 7 | Page 17

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