Hence, the vector equation of the line is given by
rr  =
λ
r
ra +
b (1)
Remark If 
ˆ
ˆ
ˆ
b
ai
bj
ck
= + +
r
, then a, b, c are direction ratios of the line and conversely,,
if a, b, c are direction ratios of a line, then 
ˆ
ˆ
ˆ
=
+
+
br
ai
bj
ck will be the parallel to
the line Here, b should not be confused with |
r
b| Derivation of cartesian form from vector form
Let the coordinates of the given point A be (x1, y1, z1) and the direction  ratios of
the line be a, b, c