1. The problem statement, all variables and given/known data we are given a neutral pion moving at 0.98c straight in the x-direction. The pions rest mass is 135MeV/c^2. two photons are emitted in opposite direction parallel to the pion's motion. I need to find the two frequencies of each photon. 2. Relevant equations m=0, E=p*c conservation of Energy E^2=(c*p)^2+(m*c^2)^2 gamma=1/sqrt(1-Beta^2) Beta = v/c p=gamma*m*v E=gamma*m*c^2 3. The attempt at a solution i know that energy and momentum are conserved but i dont know exactly what i am meant to do with the momentum relation of each pion. i keep trying all different tactics but keep going in circles. i feel like im missing something really obvious.