Class CBSE Class 12 Mathematics Applications of Derivatives Q #1844
COMPETENCY BASED
APPLY
1 Marks 2026 AISSCE(Board Exam) MCQ SINGLE
The least value of $f(x) = x^3 - 12x$, $x \in [0, 3]$ is
(A) $ -16$
(B) $ -9$
(C) $ 0$
(D) $ 16$
Correct Answer: A

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Detailed Solution

Step 1: Find the derivative

To find the critical points, we first differentiate the function $f(x) = x^3 - 12x$ with respect to $x$: $$f'(x) = 3x^2 - 12$$

Step 2: Identify critical points

Set $f'(x) = 0$ to find the critical points: $$3x^2 - 12 = 0$$ $$3(x^2 - 4) = 0$$ $$x^2 = 4 \implies x = 2, -2$$ Since the interval is $[0, 3]$, we only consider $x = 2$ as the critical point within the domain.

Step 3: Evaluate at critical points and endpoints

We evaluate $f(x)$ at the critical point $x = 2$ and the endpoints $x = 0$ and $x = 3$: $$f(0) = (0)^3 - 12(0) = 0$$ $$f(2) = (2)^3 - 12(2) = 8 - 24 = -16$$ $$f(3) = (3)^3 - 12(3) = 27 - 36 = -9$$

Step 4: Determine the least value

Comparing the values $0, -16,$ and $-9$, the minimum value is $-16$.

Final Answer: -16

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because the student must apply the First Derivative Test for local extrema and the Extreme Value Theorem for closed intervals.
Knowledge Dimension: PROCEDURAL
Justification: The question requires a step-by-step algorithmic approach involving differentiation, solving equations, and comparing values.
Syllabus Audit: In the context of CBSE Class 12, this is classified as COMPETENCY. It tests the student's ability to handle optimization problems in calculus, a core component of the 'Applications of Derivatives' unit.