1. The problem statement, all variables and given/known data I am having trouble setting up problems that require me to extremize. I know how to use Euler's equation, but I don't understand how to get what it is that I want to plug in. what I need to show is that the the correct path between two points (x,t) and (x2,t2) maximizes the proper time. and that the correct path has a constant velocity v=dx/dt 2. Relevant equations instead of distance, I am supposed to use spacetime interval dτ^2 = dt^2 − dx^2, τ is proper time 3. The attempt at a solution I tried to treat this as if it were the same as the distance equation, and the constant velocity v=dx/dt was just a constraint. but I don't know. I don't think that works. I haven't a clue how to set this up.