Question

The surface of a ball of radius A is kept at a temperature zero. If the initial temperature in the
ball is f (r), write down the boundary conditions and show that the temperature in the ball at
time t, u (r, t), is the solution to the equation:

c^2 ((∂^2 u)/(∂r^2 )+2/r ∂u/∂r)=∂u/∂t