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NDA 2025
Exam
NDA
Year
2025
Subject
Mathematics
Chapter
Continuity and Differentiability

NDA 2025 · Mathematics · Continuity and Differentiability

For the following two (02) items: Let the function f(x) = |x - 3| +...

For the following two (02) items:
Let the function f(x)=∣x−3∣+∣x−4∣f(x) = |x - 3| + |x - 4| be defined on the interval [0,5][0,5].

Consider the following statements:
I. The function is differentiable at x=3x = 3.
II. The function is differentiable at x=4x = 4.
Which of the statements given above is/are correct?

Options

  1. AI only
  2. BII only
  3. CBoth I and II
  4. DNeither I nor II

Correct answer

D. Neither I nor II

Step-by-step solution

The given function is f(x)=∣x−3∣+∣x−4∣f(x) = |x - 3| + |x - 4| defined on [0,5][0,5].

We can redefine the function by removing the absolute value signs in different intervals:

f(x)=f(x) =\begin{cases} -(x - 3) - (x - 4), & 0 \le x < 3 \\ (x - 3) - (x - 4), & 3 \le x < 4 \\ (x - 3) + (x - 4), & 4 \le x \le 5 \end{cases}<br><br>Simplifying this, we get:<br><br>$f(x) = $\begin{cases} 7 - 2x, & 0 \le x < 3 \\ 1, & 3 \le x < 4 \\ 2x - 7, & 4 \le x \le 5 \end{cases}

Differentiating f(x)f(x) with respect to xx in the open intervals:

f′(x)=f'(x) =\begin{cases} -2, & 0 < x < 3 \\ 0, & 3 < x < 4 \\ 2, & 4 < x < 5 \end{cases}$<br><br>At<br><br>Atx = 3:<br>LeftHandDerivative(LHD):<br>Left Hand Derivative (LHD)= -2<br>RightHandDerivative(RHD)<br>Right Hand Derivative (RHD)= 0<br>SinceLHD≠RHD,<br>Since LHD \neq RHD, f(x)isnotdifferentiableatis not differentiable atx = 3.<br><br>At.<br><br>Atx = 4:<br>LeftHandDerivative(LHD):<br>Left Hand Derivative (LHD)= 0<br>RightHandDerivative(RHD)<br>Right Hand Derivative (RHD)= 2<br>SinceLHD≠RHD,<br>Since LHD \neq RHD, f(x)isnotdifferentiableatis not differentiable atx = 4$.

Therefore, neither statement I nor statement II is correct.

Answer: Neither I nor II
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