1. The problem statement, all variables and given/known data A particle of mass m follows the spacetime trajectory x(τ) = (Aτ, Bτ , C cosτω, C sinτω ). What is the 4-velocity u(τ)? Why must A =sqrt[1+B^2+(ωC)^2] 2. Relevant equations u(τ)=dx(τ)/dτ , u^2 = -c^2 3. The attempt at a solution so I took the derivative of each comp of x with respect to tau and got: u(τ)=(A, B , -ωCsinτω, ωCcosτω) and 4-velocities always square to -c^2 so -A^2 +B^2 +(ωC)^2 = -c^2, which gives A =sqrt[c^2+B^2+(ωC)^2] Why is my answer wrong?