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,
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