Let A be the area of a circle with radius r. If dr/dt=5, find dA/dt when r=3. Round your answer to the nearest tenth.

Question

Let A be the area of a circle with radius r. If dr/dt=5, find dA/dt when r=3. Round your answer to the nearest tenth.

Answer 1

Area, A = πr²

dr/dt = 5

r=3

dA/dt = 2πrdr/dt

Just substitute in the values for r and dr/dt and complete and round.