1. The problem statement, all variables and given/known data Consider the vector r(t)= (1-t)i + (3+2t)j + (t-4)k which depends on scalar parameter t. For which t0 is the length of r(t0) minimal? 2. Relevant equations Equations of motion 3. The attempt at a solution So I approached this question by saying the length would be minimal when the magnitude is minimal ie. |r|=0. |r|=√[(1-t)2+(3+2t)2+(t-4)2] Simplified down I got 3t2+t+13=0 I tried using the quadratic formula to solve this then but couldn't as the value under the square root was negative. Am I approaching this question wrong then? Any help would be much appreciated.