Further, if l, m and n are the direction cosines of the given
vector, then
1
1
2
,
,
  as  | |
6
|
|
|
|
|
|
6
6
6
a
b
c
l
m
n
r
r
r
r
−
=
=
=
=
=
=
r=
r
r
r
Thus, the direction cosines are 
1
1
2
,
,–
6
6
6
⎛
⎞
⎜
⎟
⎝
⎠ 10 5 2  Vector joining two points
If P1(x1, y1, z1) and P2(x2, y2, z2) are any two points, then the vector joining P1 and P2
is the vector 
1 2
P P
uuuur  (Fig 10