If  θ = 0, then the projection vector of AB
uuur
 will be AB
uuur
 itself and if θ = π, then the
projection vector of AB
uuur
 will be BA
uuur 4 If 
= 2
π
θ
 or 
3
= 2
π
θ
, then the projection vector of AB
uuur
 will be zero vector Remark If α, β and γ are the direction angles of vector 
1
2
3 ˆ
ˆ
ˆ
a
a i
a j
a k
=
+
+
r
, then its
direction cosines may be given as
3
1
2
ˆ
cos
, cos
,  and  cos
ˆ
|
|
|
|
|
|
|
|| |
a
a
a
a i
a
a
a
a i
 
  
 
  
  
r
r
r
r
r
Also, note that |
a| cos ,  | |cos  and | |cos
a
a
α
β
γ
r
r
r
 are respectively the projections of
ar  along OX, OY and OZ