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Question

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

What is \(\frac{dy}{dx}\) at \(x = 3.5\) equal to?

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

0

To determine the derivative \(\frac{dy}{dx}\) of the function \(f(x) = |x-3| + |x-4|\) at \(x = 3.5\), let's proceed with the following step-by-step approach:

Understanding the Function

The function is given as:

\(f(x) = |x-3| + |x-4|\)

This function involves absolute values, which can be expressed as piecewise functions. Let's break it into different intervals:

  • Interval \(x < 3\)\(|x-3| = -(x-3)\) and \(|x-4| = -(x-4)\)
  • Interval \(3 \leq x < 4\)\(|x-3| = (x-3)\) and \(|x-4| = -(x-4)\)
  • Interval \(x \geq 4\)\(|x-3| = (x-3)\) and \(|x-4| = (x-4)\)

Calculating Derivative at \(x = 3.5\)

Since \(3 \leq x < 4\) when \(x = 3.5\), we consider this interval:

\(|x-3| = (x-3)\) and \(|x-4| = -(x-4)\)

Hence, on this interval:

\(f(x) = (x-3) - (x-4) = x - 3 - x + 4 = 1\)

The derivative of a constant function, such as \(1\), is:

\(\frac{d}{dx}(1) = 0\)

Conclusion

Thus, the value of \(\frac{dy}{dx}\) at \(x = 3.5\) is 0.

This result is obtained because at \(x = 3.5\), the function \(f(x)\) is a constant value, and any changes to \(x\) around this point do not result in a change in \(f(x)\). Therefore, the correct answer is \( \boxed{0} \).

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