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##### 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 ɭ^{2 }+ m^{2} +n^{2 }= 1

Direction ratios: Any three numbers that are proportional to the direction cosines of a line are called the direction ratios of the line.