1. The problem statement, all variables and given/known data Show how one can obtain the Doppler transformation for the frequency of a receding source just using the Lorentz transformations for the energy (where E=h). 2. Relevant equations Relativistic transformations for momentum and energy: E = γ(E' + vp'x) pc/E = v/c = β 3. The attempt at a solution E = γ(E' + vp'x) since p = Eβ/c, E = γ(E' + Eβ2) = γE' (1+β2). Which then would imply that = γ'(1+β2). But I have in my notes that the observed frequency = γ' (1-β). Where did I go wrong?