A n electron in an excited state in a hydrogen atom can return to the ground state in two different ways:
(a) Via a direct transition in which a photon of wavelength λ1 is emitted
(b) Via an intermediate excited state reached by the emission of a photon of wavelength λ2. This intermediate excited state then decays to the ground state by emitting another photon of wavelength λ3. Derive an equation that relates λ1 to λ2 and λ3.