1. The problem statement, all variables and given/known data A particle of rest mass m and velocity v collides elastically with a stationary particle of rest mass M. Express the recoil and scattering angels in terms of the corresponding angles in the zero-momentum system. Show that your answers reduce to the non-relativistic ones if v<<c 2. Relevant equations I think I have to show that (mc^2)/(1-(v/c)^2)^1/2 reduces to .5mv^2 by using the binomial theorem when v<<c. since momentum is related to kinetic energy. 3. The attempt at a solution (not clear how to do it though) Please help me!