The vector that goes in that direction is
Now find the unit vector in that direction - so divide it by its length...
The unit vector is
So that means that to find the coordinates of the point exactly one unit away from in the direction of , you need to add in the direction, in the direction, and subtract in the direction - in other words, add this vector to the starting point.
If you were trying to find the coordinates of any point in this line segment, multiply the unit vector by this length first, then add this resultant vector to your point.