Template:Separation of variables in two dimensions

We solve express the potential as

[math]\displaystyle{ \phi(x,z) = X(x)Z(z) }[/math]

and then Laplace's equation becomes

[math]\displaystyle{ \frac{X^{\prime\prime}}{X} = - \frac{Z{\prime\prime}}{Z} = k^2 }[/math]