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WAEC Further Mathematics 2010 Question 19

Question 19

Differentiation

Find the equation of the tangent to the curve y = 4x2 − 12x + 7 at point (2, −1).

  1. A.y + 4x − 9 = 0
  2. B.y − 4x − 9 = 0
  3. C.y − 4x + 9 = 0
  4. D.y + 4x + 9 = 0
Show the answer and explanation

Answer: C (y − 4x + 9 = 0)

Explanation

dy/dx = 8x − 12 = 4 at x = 2. Tangent: y + 1 = 4(x − 2), i.e. y − 4x + 9 = 0.