1. The problem statement, all variables and given/known data Let c be a path in R^3 with zero acceleration. Prove that c is a straight line or a point. 2. Relevant equations F(c(t)) = ma(t) a(t) = c''(t) 3. The attempt at a solution so i know that since the acceleration is zero, the velocity must be constant, and when you integrate a constant, you get a straight line...but how to I prove mathematically that the velocity is constant, because you can't integrate 0dt, as far as I know?