Hi,
i'd appriate if any1 cud solve this doubt, found in O/N09 P31
In a model of the expansion of a sphere of radius r cm, it is assumed that, at time t seconds after the
start, the rate of increase of the surface area of the sphere is proportional to its volume. When t = 0,
dr
r = 5 and - = 2.
dt
(i) Show that r satis?es the differential equation
dr 2
- = 0.08r .
dt
2
[The surface area A and volume V of a sphere of radius r are given by the formulae A = 4(Pi)r ,
4 3
V = - (Pi)r .]
3
