3, one may note that the triangle OAP is right angled, and in it, we
have 
(
)
cos
 
 stands for | |
x
r
r
α =r
r Similarly, from the right angled triangles OBP and
OCP, we may write cos
y and cos
z
r
r
β =
γ = Thus, the coordinates of the point P may
also be expressed as (lr, mr,nr) The numbers lr, mr and nr, proportional to the direction
cosines are called as direction ratios of vector rr , and denoted as a, b and c, respectively