If 
2
   
 then 
|
||
|
a
b
a b
 
r 
r
r
r 4 In view of the Observations 2 and 3, for mutually perpendicular
unit vectors 
ˆ
ˆ
,ˆ
and
i
j
k  (Fig 10 24), we have
ˆ
ˆ
i
i
×  = 
ˆ
ˆ
ˆ
ˆ
0
j
j
k
k
×
=
×
=
r
ˆ
ˆ
i
×j
= ˆ
ˆ
ˆ
ˆ
ˆ
ˆ
ˆ
,
,  
k
j
k
i
k
i
j
×
=
× =
5