If the direction cosines between two lines are given by the relations al+bm+cn=0 and hlm+fmn+gnl=0, then the two lines are parallel. ifaf±bg±ch+−4=

If the direction cosines between two lines are related by the relations al+bm+cn=0and hlm+fmn+gnl=0, then the condition that the lines are to be parallel isaf±bg±ch=0It implies that af±bg±ch+−4=0+2i=2i