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

The angle between the lines whose direction cosines satisfy the equations l+m+n=0 " and " l^(2)=m^(2)+n^(2) is

Find the angle between the lines whose direction cosines satisfy the equaitons l + m + n = 0, l^(2) + m^(2) - n^(2) = 0 .