Question 1000520
"Ship A has position vector (9 i + 3 j) km" means that the map of whoever maps ships and assigns ship positions looks like this
{{{drawing(400,300,-2,13.3,-2,8,
grid(1),red(line(10.2,5,10.2,7.5)),
red(arrow(10.2,5,10.2,7.5)),locate(10.5,7.8,red(N)),
blue(arc(9,3,0.8,0.2,0,360)),blue(arc(9,3,0.6,0.1,0,360)),
locate(9,2.7,blue(ship)),locate(10.4,2.7,blue(A)),
blue(line(0,0,9,3)),blue(arrow(6,2,8.7,2.9)),
locate(4.5,1.5,blue(position)),locate(7,1.5,blue(vector))
)}}}
(I am assuming that for assigning position vectors, the y-axis (or j-axis) points North,
and that applies to the absolute position of a ship,
and to its position relative to another ship).
"Relative to an observer on a second ship B, ship A has position vector (-9i-2j) km" means that the map with both ships looks like this
{{{drawing(600,225,-2,22,-2,7,
grid(1),red(line(20.2,4,20.2,6.5)),
red(arrow(20.2,4,20.2,6.5)),locate(20.5,7,red(N)),
blue(arc(9,3,0.8,0.2,0,360)),blue(arc(9,3,0.6,0.1,0,360)),
locate(9,2.7,blue(ship)),locate(10.4,2.7,blue(A)),
blue(line(0,0,9,3)),blue(arrow(6,2,8.7,2.9)),
red(arc(18,5,0.8,0.2,0,360)),red(arc(18,5,0.6,0.1,0,360)),
locate(18,4.7,red(ship)),locate(19.5,4.7,red(B)),
red(line(18,5,9.2,3.1)),red(arrow(13.5,4,9.2,3.1)),
locate(4.5,1.5,blue((9i+3j))),locate(13.5,4,red((-9i-2j)))
)}}}
The absolute position vector for ship B would be
{{{blue((9i+3j))-red((-9i-2j))=highlight((18i+5j))}}}