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Question

Consider the following statements regarding the function \(f(x) = \frac{1}{x-5}\)

Statement-I :
\(f(x)\) is decreasing on the intervals \(x < 5\) and \(x > 5\).

Statement-II :
\(f'(x) > 0\) for all \(x \neq 5\).

Which one of the following is correct in respect of the above statements?

This question was previously asked in
NDA 2 2025 GAT Question Paper (14-Sep-2025)
The correct answer is

Statement-I is correct but Statement-II is not correct

To determine the correctness of the given statements about the function \(f(x) = \frac{1}{x-5}\), we need to analyze the behavior of this function.

Step-by-Step Analysis:

  • Critical Point and Domain:
    • The function \(f(x) = \frac{1}{x-5}\) is undefined when \(x = 5\) because the denominator becomes zero.
    • The domain of the function is \(x \neq 5\).
  • Statement-I Analysis:
    • The function \(f(x)\) can be analyzed separately for the intervals \(x < 5\) and \(x > 5\).
    • To check for monotonicity (increasing/decreasing behavior), compute the derivative \(f'(x)\):

\(f'(x) = \frac{-1}{(x-5)^2}\)

  •  
    • The derivative \(f'(x) = \frac{-1}{(x-5)^2}\) is always negative for all \(x \neq 5\) since the square of any real number is positive, and dividing -1 by a positive number results in a negative value.
    • This implies \(f(x)\) is decreasing on both intervals: \(( -\infty, 5 )\) and \(( 5, \infty )\).
    • Thus, Statement-I is correct.
  • Statement-II Analysis:
    • Statement-II claims \(f'(x) > 0\) for all \(x \neq 5\). However, from our computation, \(f'(x) = \frac{-1}{(x-5)^2}\) is negative for all \(x \neq 5\).
    • This invalidates Statement-II because the derivative is not positive.

Conclusion:

  • Statement-I is correct as \(f(x)\) is decreasing on both specified intervals.
  • Statement-II is incorrect since \(f'(x)\) is negative for all defined \(x\).

Thus, the correct answer is: Statement-I is correct but Statement-II is not correct.

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