Reunification is a ...

Don't sell yourself short, give yourself a positive psychological hint, so that you can be in an invincible position when doing math problems.

The algorithm of vector AB is that the abscissa of B minus the abscissa of A and the ordinate of B minus the ordinate of A, so it is (4- 1,-1-3)=(3). -4).

The length of the vector is the sum of the squares of the components in brackets, and then the root sign is opened. Take a positive number, because 3 2+(-4) 2 = 25 = 5 2, so it is 5, indicating the meaning of the index.

Then there is the problem of unitization. (3.-4) Divide each number by the length of the vector to get (3/5, -4/5). Choose a.