Nevertheless, we shall also translate
these results in the Cartesian form which, at times, presents a more clear geometric
and analytic picture of the situation 11 2  Direction Cosines and Direction Ratios of a Line
From Chapter 10, recall that if a directed line L passing through the origin makes
angles α, β and γ with x, y and z-axes, respectively, called direction angles, then cosine
of these angles, namely, cos α, cos β and cos γ are called direction cosines of the
directed line L If we reverse the direction of L, then the direction angles are replaced by their supplements,
i