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The function f x = x 3 - a x has a local minimum at x = k , where k ≥ 2, then a possible value of a is

Options

  1. A9
  2. B11
  3. C13
  4. D8

Correct answer

C. 13

Step-by-step solution

f ' x = 3 x 2 - a = 0 ⇒ x = ± a 3 ∴ f ( x ) has local minimum at x = + a 3   ⇒ a 3 ≥ 2 ⇒ a ≥ 1 2

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