Thank you for your comment. I obtain the following using Solve: If I try to write the conditions on the constant I obtain the same mistake as in FindInstance. Now, if I don't write the conditions for the constants, then I obtain a solution but some of the constants
$n,a,b,c_1, c_2$ has assigned values. However, using SetAttributes[{n,a,b,c1,c2}, Constant] and only writting the conditions for the constants, the mistake was fixed and I obtain conditional expressions in terms of
$n,a,b,c_1,c_2$.
Edit: Solve works writing only the conditions for the constants, and in the solution some of them has assigned values in terms of other constants.
