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JAMB Mathematics 1992 Question 39

Question 39

Differentiation

Obtain a maximum value of the function f(x) = x3 − 12x + 11

  1. A.−5
  2. B.−2
  3. C.2
  4. D.27
Show the answer and explanation

Answer: D (27)

Explanation

f′(x) = 3x2 − 12 = 0 gives x = ±2. f″(−2) = −12 < 0, so the maximum is at x = −2: f(−2) = −8 + 24 + 11 = 27.