related rates (one forumla)

Question

The radius of a circle is decreasing at a constant rate of 3 inches per minute. At the instant when the radius of the circle is 8 inches, what is the rate of change of the area? Round your answer to three decimal places.

Answer 1

Area A = πr²; dA/dt = 2πrdr/dt = 2π·8inch·(- 3)inch/min = - 150.796 inch²/min