Using distance formula (from Class XI), the magnitude of OP
uuur  (or rr ) is given by
| OP |
uuur  =
2
2
2
x
y
z
+
+
In practice, the position vectors of points A, B, C, etc , with respect to the origin O
are denoted by ar , ,
b c
r r , etc , respectively (Fig 10 2 (ii))