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JAMB Mathematics 1999 Question 40

Question 40

Differentiation

If the maximum value of y = 1 + hx − 3x2 is 13, find h.

  1. A.13
  2. B.12
  3. C.11
  4. D.10
Show the answer and explanation

Answer: B (12)

Explanation

dy/dx = h − 6x = 0 at x = h/6. Then y = 1 + h²/6 − h²/12 = 1 + h²/12 = 13, so h² = 144 and h = 12 (taking the positive value offered).