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JAMB Mathematics 2002 Question 11

Question 11

Differentiation

A circle with a radius 5cm has its radius increasing at the rate of 0.2cms−1. What will be the corresponding increase in the area?

  1. A.2π
  2. B.5π
  3. C.π
  4. D.4π
Show the answer and explanation

Answer: A (2π)

Explanation

A = πr2, so dA/dt = 2πr × dr/dt = 2π × 5 × 0.2 = 2π cm2 per second.