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WAEC Further Mathematics 2010 Question 34

Question 34

Integration

Given that dy/dx = 3x2 − 4 and y = 6 when x = 3, find y.

  1. A.x3 − 4x − 9
  2. B.x3 − 4x + 9
  3. C.x3 + 4x − 9
  4. D.x3 + 4x + 9
Show the answer and explanation

Answer: A (x3 − 4x − 9)

Explanation

y = x3 − 4x + c. When x = 3: 27 − 12 + c = 6, so c = −9 and y = x3 − 4x − 9.