The points (x, y) that remain fixed for all t are solutions of the equation Umn(x, y, t) = 0 for all t > 0. Thus to determine the nodal lines it is enough to solve the equation
The points (x, y) that remain fixed for all t are solutions of the equation Umn(x, y, t) = 0 for all t > 0. Thus to determine the nodal lines it is enough to solve the equation