(a) Show that the Onsager quantization condition (14.13) (with λ=21) applied to the orbits of a free electron leads directly to the free electron levels (14.2).
(b) Show that the degeneracy (14.4) of the free electron levels (14.2) is just the number of zero-field free electron levels with the given kz, and with kx and ky within a planar region of area ΔA (Eq. (14.12)).