� The magnitude (r), direction ratios (a, b, c) and direction cosines (l, m, n) of
any vector are related as:
,
,
a
b
c
l
m
n
r
r
r
=
=
=
� The vector sum of the three sides of a triangle taken in order is 0
r © NCERT
not to be republished
 MATHEMATICS
460
� The vector sum of two coinitial vectors is given by the diagonal of the
parallelogram whose adjacent sides are the given vectors � The multiplication of a given vector by a scalar λ, changes the magnitude of
the vector by the multiple |λ|, and keeps the direction same (or makes it
opposite) according as the value of λ is positive (or negative) � For a given vector ar , the vector ˆ
|
a|
a
=a
r
r  gives the unit vector in the direction
of ar