1. The problem statement, all variables and given/known data An inertial observer O bounces a radar signal off an arbitrary event P. If the signal is emitted and received by O at times τ1 and τ2 respectively, as indicated by O’s clock, prove that the squared interval ∆s 2 between O’s origin event (i.e., its spatial origin at time τ = 0) and P is c 2 τ1τ2. 2. Relevant equations ∆s^2=ct^2-|r|^2 3. The attempt at a solution u'=γ(u1-βu4)?? I am not even sure if I need to do a Lorentz transformation. Please give me some direction!