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JAMB Mathematics 2013 Question 37

Question 37

Differentiation

The radius of a circle is increasing at the rate of 0.02 cms−1. Find the rate at which the area is increasing when the radius of the circle is 7 cm.

  1. A.0.35cm2s−1
  2. B.0.88cm2s−1
  3. C.0.75cm2s−1
  4. D.0.55cm2s−1
Show the answer and explanation

Answer: B (0.88cm2s−1)

Explanation

dA/dt = 2πr × dr/dt = 2 × 22/7 × 7 × 0.02 = 0.88 cm2/s.