Answer:
formula for the area A of a circle in terms of its radius r:
A = πr2
It is important to remember that both r, and hence, A are functions of time, t. Take the derivative of both sides with respect to t and obtain
dA/dt = 2πr(dr/dt)
Note that we are using implicit differentiation here, since A and r are (implicit) functions of t. Now we can find the required answers.
r = 5 inches.
Substitute r = 5 and dr/dt = 3 to get
dA/dt = 2π5·3 = 30π ≅ 95.25
(the units are in2/min.)
r = 22 inches
dA/dt = 2π22·3 = 132π ≅ 414.69
Hope that helps.
