Three Dimension Geometry – Notes
Direction Cosines and Direction Ratios
Directional angles: The angles made by a line with the positive directions of the X, Y and Z axes are called directional angles.
Directional Cosines: If a , b and g are the directional angles of a directed line L, them cos a, cos b, and cos g , are called the directional cosines of the directed line L.
If ɭ, m, n are the directional cosines of a line, then ɭ2 + m2 +n2 = 1
Direction ratios: Any three numbers that are proportional to the direction cosines of a line are called the direction ratios of the line.