® Direction cosines of a line are the cosines of the angles made by the line

® Direction cosines of a line are the cosines of the angles made by the line with the positive directions of the coordinate axes. ® If l , m , n are the direction cosines of a line, then l + m + n = . ® Direction cosines of a line joining two points P( x , y , z ) and Q( x , y , z ) are where PQ =