Question:medium

Evaluate the definite integral: \( \displaystyle \int_{3}^{5} |x-4|\,dx \).

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When integrating absolute value functions, always split the interval at the point where the expression inside the modulus becomes zero.
Updated On: Apr 16, 2026
  • \(1\)
  • \(2\)
  • \(3\)
  • \(4\)
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The Correct Option is B

Solution and Explanation

To evaluate the definite integral \( \int_{3}^{5} |x-4| \, dx \), we need to handle the absolute value function carefully by understanding where the expression inside the absolute value changes sign.

The expression inside the absolute value is \( x - 4 \). This expression changes sign at \( x = 4 \). Therefore, we break the integral at this point:

  1. For \( 3 \leq x < 4 \), \( |x-4| = -(x-4) = 4-x \).
  2. For \( 4 \leq x \leq 5 \), \( |x-4| = x-4 \).

We split the integral \(\int_{3}^{5} |x-4| \, dx\) into two parts:

\(\int_{3}^{5} |x-4| \, dx = \int_{3}^{4} (4 - x) \, dx + \int_{4}^{5} (x - 4) \, dx\)

Let's evaluate these two integrals separately.

First Integral: \(\int_{3}^{4} (4 - x) \, dx\)

Compute the antiderivative: The integral of \(4-x\) is \((4x - \frac{x^2}{2})\).

Evaluate from 3 to 4:

\[ \left[4x - \frac{x^2}{2}\right]_{3}^{4} = \left(4(4) - \frac{4^2}{2}\right) - \left(4(3) - \frac{3^2}{2}\right) \] \[ = \left(16 - 8\right) - \left(12 - 4.5\right) \] \[ = 8 - 7.5 = 0.5 \]

Second Integral: \(\int_{4}^{5} (x - 4) \, dx\)

Compute the antiderivative: The integral of \(x-4\) is \(\left(\frac{x^2}{2} - 4x\right)\).

Evaluate from 4 to 5:

\[ \left[\frac{x^2}{2} - 4x\right]_{4}^{5} = \left(\frac{5^2}{2} - 4(5)\right) - \left(\frac{4^2}{2} - 4(4)\right) \] \[ = \left(\frac{25}{2} - 20\right) - \left(8 - 16\right) \] \[ = \left(12.5 - 20\right) - \left(-8\right) \] \[ = -7.5 + 8 = 0.5 \]

Add the Results of Both Integrals:

\(0.5 + 0.5 = 1\)

Thus, the value of the definite integral \( \int_{3}^{5} |x-4| \, dx \) is 1, which seems to suggest a discrepancy since the expected answer is provided as 2. Upon rechecking, it confirms that the calculations imply a conceptual miscalculation in step understanding which showed nominal result pre-discussed. Hence, this computed answer is accurate as per logical structure.

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