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WAEC Further Mathematics 2012 Question 15

Question 15

Differentiation

If y = x3 − x2 − x + 6, find the values of x at the turning points.

  1. A.½, −3
  2. B.⅓, ½
  3. C.1, −⅓
  4. D.1, ⅓
Show the answer and explanation

Answer: C (1, −⅓)

Explanation

dy/dx = 3x2 − 2x − 1 = (3x + 1)(x − 1) = 0 at turning points, so x = 1 or x = −⅓.