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WAEC Further Mathematics 2026 Question 25

Question 25

Differentiation

Find the maximum value of the curve y = 2x3 + 4x2 − 8x − 4

  1. A.8
  2. B.12
  3. C.20
  4. D.28
Show the answer and explanation

Answer: B (12)

Explanation

dy/dx = 6x² + 8x − 8 = 0 gives 3x² + 4x − 4 = 0, (3x − 2)(x + 2) = 0. d²y/dx² = 12x + 8 is negative at x = −2, so the maximum is y = −16 + 16 + 16 − 4 = 12.