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NDA 2025
Exam
NDA
Year
2025
Subject
Mathematics
Chapter
Application of Derivatives

NDA 2025 · Mathematics · Application of Derivatives

For the following two (02) items: Consider the function f(x) = 1 -...

For the following two (02) items:
Consider the function f(x)=1−(x−1)23f(x) = 1 - \sqrt[3]{(x-1)^2}.

The function has

Options

  1. Aa minimum at x=1x = 1
  2. Ba maximum at x=1x = 1
  3. Cneither maximum nor minimum at x=1x = 1
  4. Dno extremum

Correct answer

B. a maximum at x=1x = 1

Step-by-step solution

Given f(x)=1−(x−1)2/3f(x) = 1 - (x-1)^{2/3}

Differentiating with respect to xx:

f′(x)=−23(x−1)−1/3=−23(x−1)1/3f'(x) = -\dfrac{2}{3}(x-1)^{-1/3} = \dfrac{-2}{3(x-1)^{1/3}}

For x<1x < 1, x−1<0⇒f′(x)>0x-1 < 0 \Rightarrow f'(x) > 0. Thus, f(x)f(x) is strictly increasing.

For x>1x > 1, x−1>0⇒f′(x)<0x-1 > 0 \Rightarrow f'(x) < 0. Thus, f(x)f(x) is strictly decreasing.

Since f′(x)f'(x) changes sign from positive to negative as xx passes through 11, f(x)f(x) has a local maximum at x=1x = 1.

Alternatively, (x−1)2/3≥0(x-1)^{2/3} \geq 0 for all real xx.

1−(x−1)2/3≤11 - (x-1)^{2/3} \leq 1

f(x)≤f(1)f(x) \leq f(1) for all xx.

Hence, f(x)f(x) has a maximum at x=1x = 1.

Answer: a maximum at x=1x = 1
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