Question

if two displacements vectors add to yield a total displacement of 0, what do you know about the two displacements

Answer 1

equal and opposite way

Answer 2

See look if you add two vectors and they equal 0 there diagonal equals 0.
See:

If you add two vectors that are equal and opposite to each other you get 0.

Answer 3

Here i put them ened to end to add them
As you can see there is no resulting vector so the net displacement is 0.