Breit-Wigner form of a transmission resonance the purpose of this problem is to derive (33) from (29). 

(a) By expanding the cosine for small phase differences away from resonance, δφ = φ – 2πn, find a simplified form of (29) involving only |t₁|², |t₂|², and δφ. 

(b) Show that, for states in a 1D box, the following relation holds between small changes in the phases and small changes in the energy: δε/Δε = δφ/2π where Δε is the level spacing. 

(c) Combine (a) and (b) to obtain (33)