Many thanks to both of you for the information but I still have the problem.:)
I have tried what both of you have written and I can not find an answer.
In the first case I can't get an "out", it says:
*SetDelayed::Write: Tag In in ln is protected.
In the second case I obtain:
*DSolve::bvimp: General solution contains implicit solutions. In the boundary value problem these solutions will be ignored, so some of the solutions will be lost.
Attachment: Duda.nb, URL: ,