Angle between line if relation between direction cosine is given

An angle between the lines whose direction cosines are given by the equations, 1+ 3m + 5n =0 and 5 lm - 2m n + 6 nl =0, is :

The angle between the straight lines, whose direction cosines are given by the equations 2l+2m -n=0 and mn+nl+lm=0 , is :

The angle between the lines whose direction cosines are given by the equatios l^2+m^2-n^2=0, m+n+l=0 is

Find the angle between the lines whose direction cosine are given by the equation: "l"-"m"+"n"=0" and l"^2-"m"^2-"n"^2=0

The angle between the lines whose direction cosines are given by 3l+4m+5n=0 , l^(2)+m^(2)-n^(2)=0 is

Find the angle between the lines whose direction cosines are given by the equations 3l+m+5n=0 and 6mn-2nl+5lm=0

Show that the angle between the straight lines whose direction cosines are given by the equation l+m+n=0 and amn+bnl+clm=0 is pi/3 if 1/a+1/b+1/c=0