A circular oilspill is spreading such that the radius is increasing at 0.5 metres per minute. Find the rate of increase of the are of the oil spill when the radius is 10m.
a = pi r^2
da/dt = 2pi r dr/dt
Now plug in r and dr/dt to get da/dt.
da/dt = 2pi r dr/dt
Now plug in r and dr/dt to get da/dt.