%0 Journal Article %T Dirichlet and Neumann Problems for String Equation, Poncelet Problem and Pell-Abel Equation %A Vladimir P. Burskii %A Alexei S. Zhedanov %J Mathematics %D 2006 %I arXiv %R 10.3842/SIGMA.2006.041 %X We consider conditions for uniqueness of the solution of the Dirichlet or the Neumann problem for 2-dimensional wave equation inside of bi-quadratic algebraic curve. We show that the solution is non-trivial if and only if corresponding Poncelet problem for two conics associated with the curve has periodic trajectory and if and only if corresponding Pell-Abel equation has a solution. %U http://arxiv.org/abs/math/0604278v1