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WAEC Further Mathematics 2006 Question 27

Question 27

Differentiation

Find the least value of the function f(x) = 3x2 + 18x + 32.

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

Answer: A (5)

Explanation

f'(x) = 6x + 18 = 0 at x = −3. f(−3) = 27 − 54 + 32 = 5, and since the x² coefficient is positive this is the least value.