Question

How can I solve this? The radius of a circular puddle is growing at a rate of 20 cm/s How fast is the area growing at the instant when it equals 1 cm^2?

Answer 1

formula for the area is \(A=\pi r^2\)

Answer 2

take the derivative and get
\[A'=2\pi r r'\]
you are asked for \(A'\) and told \(r'=20\) and \(r=1\) so you can find \(A'\)

Answer 3

do I just plug in 20 into the equation?