12 Fig 10 12
When λ = –1, then a
λ = −a
r
r, which is a vector having magnitude equal to the
magnitude of ar  and direction opposite to that of the direction of ar The vector – ar  is
called the negative (or additive inverse) of vector ar  and we always have
(– )
a
a
r+
r  = (– )
0
a
+a
=
r
r
r
Also, if 
= |1
a|
λ
r , provided 
0,  i