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WAEC Further Mathematics 2023 Question 28

Question 28

Differentiation

Find the equation of the normal to the curve y = 3x2 + 2 at point (1, 5).

  1. A.6y − x − 29 = 0
  2. B.6y + x − 31 = 0
  3. C.y − 6x + 1 = 0
  4. D.y − 6x − 1 = 0
Show the answer and explanation

Answer: B (6y + x − 31 = 0)

Explanation

dy/dx = 6x = 6 at x = 1, so the normal has gradient −1/6. y − 5 = −(x − 1)/6 gives 6y + x − 31 = 0.