and 
in the directions of the 
-axis and 
-axis respectively. In three dimensions the three unit vectors are usually denoted 
[M2.5]
are: unit vectors in the mutually perpendicular directions of the Cartesian coordinate axes. Two such vectors are required in two dimensions, usually denoted by and in the directions of the -axis and -axis respectively. In three dimensions the three unit vectors are usually denoted [M2.5]
Copyright 1997, The Open University