JEE MainMathematicsLimits Continuity and DifferentiabilityMCQ+4 / −1
Consider the function defined by . If and be respectively the number of points at which is not continuous and is not differentiable, then is
- A0
- B1
- C2
- D3
View written solutionFree
Correct answer: B
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Given function
Since , write
\ln x|}.$$
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Remove the absolute value by cases
We know:
- If , then , so .
- If , then , so .
Therefore,
\begin{cases} e^{-(-\ln x)}=e^{\ln x}=x, & 0<x<1,\\[4pt] e^{-\ln x}=\dfrac{1}{x}, & x\ge 1. \end{cases}$$ So, $$f(x)= \begin{cases} x, & 0<x<1,\\ \dfrac{1}{x}, & x\ge 1. \end{cases}$$ -
Check continuity
On , , which is continuous.
On , , which is continuous.
The only possible issue is at .
- Left limit:
- Right limit:
- Function value:
\ln 1|}=e^0=1.$$
Hence is continuous at as well.
Therefore, the number of points where is not continuous is
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Check differentiability
On ,
On ,
Again, only needs checking.
- Left derivative at :
- Right derivative at :
Since is not differentiable at .
Therefore, the number of points where is not differentiable is
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Compute
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Match with options
Option B: 1 is correct.
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