​ @CPhill

I think heureka answered this here :

https://web2.0calc.com/questions/correct#r2

The vector in the opposite direction of  $\vec u$  is  $-\vec u$  .

The unit vector in the same direction of  $\vec u$  is  $\frac{\vec u}{|\vec u|}$  which is  $\frac{\vec u}{7}$  .

So the unit vector in the opposite direction of  $\vec u$  is  $-\frac{\vec u}{7}$  .