If f(x) = x³ − 12x² + 36x + 17 is decreasing, then x belongs to:
If f(x) = x³ − 12x² + 36x + 17 is decreasing, then x belongs to:
- A. (2, 6)
- B. (−∞, 2) ∪ (6, ∞)
- C. (−∞, 2)
- D. (6, ∞)
Answer: A) (2, 6)
Explanation: f'(x) = 3x² − 24x + 36 = 3(x² − 8x + 12) = 3(x − 2)(x − 6). f'(x) < 0 → (x − 2)(x − 6) < 0 → 2 < x < 6.
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