The position function of a particle is given by r(t)=⟨−5t2,−4t,t2+1t⟩. At what time is the speed minimum? I found the speed function by taking the magnitude of the velocity which is lv(t)l = sqrt(108t^2 +4t + 17) I then took the derivative of the speed to find the critical point. However, I'm always left with a negative time. d/dt lv(t)l = (104t + 2)/sqrt(104t^2 +4t+17) The only way to find the minimum is when the numerator is 0. But when I isolate t, it always equals a negative number. Is my approach correct? Any help would be appreciated. Thanks!