Then
(i)
(
)
ka
ma
k
m a
+
=
+
r
r
r
(ii)
(
)
(
)
k ma
r=km a
r
(iii)
(
)
k a
b
ka
kb
 
 
 
r
r
r
r
Remarks
(i)
One may observe that whatever be the value of λ, the vector a
λr  is always
collinear to the vector ar In fact, two vectors  and 
a
rb
r
 are collinear if and only
if there exists a nonzero scalar λ such that b
r= λa
r If the vectors 
a and 
rb
r
 are
given in the component form, i e