The direction cosines l, m and n of two lines are connected by the relations `l+m+n=0 and lm=0`, then the angle between the lines is

The direction cosines l, m, n of two lines are connected by the relation l+m+n=0 and l . m=0 then the angle between them is

If the d.c.'s (l, m, n) of two lines are connected by the relations l+m+n=0 " and " 2mn+3ln-5lm=0 then the angle between the lines is

If the d.c.'s (l, m, n) of two lines are connected by the relations 3l+m+5n=0, 6mn-2nl+5lm=0 then the angle between the lines is

If the d.c.'s (l, m, n) of two lines are connected by the relations l+m-n=0, 12lm-mn-6 1n=0 then the angle between the lines is

If the d.c's (l,m,n) of two lines are connected by the relations 3l+m+5n=0, 6mn - 2nl + 5lm=0 then the angle between the lines is

If the direction cosines of two lines are connected by the equations l+m+n=0 and l^(2) + m^(2) -n^(2)=0 , then the angle between these lines is of measure