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WAEC Further Mathematics 2009 Question 3

Question 3

Differentiation

The line y = mx − 3 is a tangent to the curve y = 1 − 3x + 2x3 at the point (1, 0). Find the value of the constant m.

  1. A.−4
  2. B.−1
  3. C.3
  4. D.4
Show the answer and explanation

Answer: C (3)

Explanation

dy/dx = −3 + 6x2. At x = 1 the gradient is 3, so m = 3 (and y = 3x − 3 does pass through (1, 0)).