Direction ratios provide a convenient way of specifying the direction of a line in three dimensional
space.
For any vector r = ai + bj, its direction ratio is a : b
Given a vector r = ai + bj + ck its direction ratios are a : b : c. This means that to move in
the direction of the vector we must must move a units in the x direction and b units in the y
direction for every c units in the z direction.