In the method of separation of variables (Section 4.2) for two-dimensional, steady-state conduction, the separation constant 2

In the method of separation of variables (Section 4.2) for two-dimensional, steady-state conduction, the separation constant λ2 in Equations 4.6 and 4.7 must be a positive constant. Show that a negative or zero value of A 2 will result in solutions that cannot satisfy the prescribed boundary conditions.