Let A be the area of a circle with radius r. If dr/dt=4, find dA/dt when r=5

Answer 1

List given information

A = πr²

dr/dt = 4

r = 5

dA/dt = ?

Determine dA/dt when r=5

A = πr²

dA/dt = 2πr(dr/dt)

dA/dt = 2π(5)(4)

dA/dt = 2π(20)

dA/dt = 40π

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