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WAEC Further Mathematics 2021 Question 34

Question 34

Differentiation

Find the equation of the normal to the curve y = 2x2 − 5x + 10 at P(1, 7).

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

Answer: C (y − x − 6 = 0)

Explanation

dy/dx = 4x − 5 = −1 at x = 1, so the normal has gradient 1. y − 7 = x − 1 gives y − x − 6 = 0.