passwella.
Menu

WAEC Further Mathematics 2016 Question 29

Question 29

Differentiation

The radius of a circle increases at a rate of 0.5 cms−1. Find the rate of change in the area of the circle with radius 7 cm. [Take π = 22/7]

  1. A.11 cm2s−1
  2. B.22 cm2s−1
  3. C.33 cm2s−1
  4. D.44 cm2s−1
Show the answer and explanation

Answer: B (22 cm2s−1)

Explanation

dA/dt = 2πr dr/dt = 2 × 22/7 × 7 × 0.5 = 22 cm²s⁻¹.