Solve the following Laplace's equation in a cube, carefully explaining all steps. Separate the variables using two steps: first, separate (x, y) from z and then separate x from y:
u(x, y, z) = ∑Γ ̠̐(x, y) h(z) = ∑Γ ̐(x) ̑(y) h(z).
When solving the boundary value problems (Sturm-Liouville problems) for ̐(x) and ̑(y), make sure to check for zero eigenvalues. Note that the single non-homogeneous boundary condition is on the z-plane, z = 0. The boundary conditions are simple enough so that all Fourier coefficient integrals are easily calculated. Many steps are very similar to the equation of a vibrating membrane solved in class:
∇²u = ∂²u/∂x² + ∂²u/∂y² + ∂²u/∂z² = 0 (0 < x < 1, 0 < y < 1, 0 < z < 1)
u(0, y, z) = ∂u/∂x(1, y, z) = 0
∂u/∂y(x, 0, z) = ∂u/∂y(x, 1, z) = 0
u(x, y, 0) = 1; u(x, y, 1) = 0