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NDA 2020
Exam
NDA
Year
2020
Subject
Mathematics
Chapter
Continuity and Differentiability

NDA 2020 · Mathematics · Continuity and Differentiability

Consider the following statements for f(x)=e^ -|x| : 1. The...

Consider the following statements for f(x)=e−∣x∣f(x)=e^{-|x|} : 1. The function is continuous at x=0x=0. 2. The function is differentiable at x=0x=0. Which of the above statements is/are correct?

Options

  1. A1 only
  2. B2 only
  3. CBoth 1 and 2
  4. DNeither 1 nor 2

Correct answer

A. 1 only

Step-by-step solution

(1) f(x)=e−∣x∣,f(0)=e−∣0∣=1f(x)=e^{-|x|}, f(0)=e^{-|^{0}|}=1. f(x)=e−x, for  x≥0=ex, for x<0\begin{gathered} f(x)=e^{-x}, \text{\text{ for } } x \geq 0 \\ =e^x, \quad \text{ for } x < 0 \end{gathered}LHL=lim⁡x→0−f(x)=lim⁡x→0−ex=1RHL=lim⁡x→0+f(x)=lim⁡x→0+e−x=1\begin{aligned} & \mathrm{LHL}=\lim _{x \rightarrow 0^{-}} f(x)=\lim _{x \rightarrow 0^{-}} e^x=1 \\ & \mathrm{RHL}=\lim _{x \rightarrow 0^{+}} f(x)=\lim _{x \rightarrow 0^{+}} e^{-x}=1\end{aligned}$As,As,f(0)=LHL=RHL\mathrm{LHL}=\mathrm{RHL} Thus f(x)f(x) is continuous at x=0x=0. (2) \mathrm{LHD}=\lim _{x \rightarrow0^{-}} f^{\prime}(x)=\lim _{x \rightarrow0^{-}} e^x=e^0=1\mathrm{RHD}=\lim _{x \rightarrow0^{+}} f^{\prime}(x)=\lim _{x \rightarrow0^{+}}-e^{-x}=-e^0=-1 As LHD ≠ RHD Hence, f(x)f(x) is not differentiable at x=0x=0.$
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