Question:medium

Let \( f(x) = x^3 - 6x^2 + 12x - 3 \), then at \( x = 2 \), \( f(x) \) has:

Updated On: Mar 27, 2026
  • a maximum
  • a minimum
  • both a maximum and a minimum
  • neither a maximum nor a minimum
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The Correct Option is B

Solution and Explanation

To ascertain if \( f(x) = x^3 - 6x^2 + 12x - 3 \) possesses a maximum or minimum at \( x = 2 \), calculus, specifically the first and second derivative tests, is employed.

1. First Derivative Computation: The first derivative, \( f'(x) \), is calculated.

\[ f'(x) = \frac{d}{dx}(x^3 - 6x^2 + 12x - 3) = 3x^2 - 12x + 12 \]

2. Identification of Critical Points: \( f'(x) \) is set to zero to solve for \( x \).

\[ 3x^2 - 12x + 12 = 0 \]

Dividing the equation by 3 yields:

\[ x^2 - 4x + 4 = 0 \]

This equation factors as a perfect square:

\[ (x - 2)^2 = 0 \]

Consequently, \( x = 2 \) is identified as a critical point.

3. Second Derivative Calculation: The second derivative, \( f''(x) \), is determined to classify the critical point.

\[ f''(x) = \frac{d}{dx}(3x^2 - 12x + 12) = 6x - 12 \]

The value of \( f''(x) \) is evaluated at the critical point \( x = 2 \).

\[ f''(2) = 6(2) - 12 = 0 \]

4. Determination of Nature of Critical Point: The second derivative test proves inconclusive as \( f''(2) = 0 \). However, the presence of a double root in the first derivative at \( x = 2 \) indicates a point where the function's graph exhibits a horizontal tangent. Further analysis, such as the first derivative test or examining sign changes in \( f'(x) \) around \( x = 2 \), is recommended. Given the cubic nature of \( f(x) \), a transition from increasing to decreasing or vice versa is expected at \( x = 2 \), suggesting a minimum.

Therefore, \( f(x) \) has a minimum at \( x = 2 \).

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