Displacement vector

The displacement vector of the particle is given by,

Δr = (x2 – x1 )i + (y2 – y1 )j + (z2 – z1 )k

Magnitude of Δ r is given by

| Δ r | = [ (x2 – x1 )2 + (y2 – y1 )2 + (z2 – z1 )2 ]1/2