This is a question in the book to solve Heat Problem
With 0<r<1, , t>0. And
The solution manual gave this which I don't agree:
What the solution manual did is for , it has to assume in order using Dirichlet problem to get (1a) shown in the scanned note.
I think it should use the complete solution shown in (2a), then let t=0 where
I don't agree with the first part as I don't think you can assume . Please explain to me.