Angle between line if relation between direction cosine is given

Find the angle between the two lines whose direction cosines are given by the equation l+m+n=0,2l+2m-mn=0

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

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

Find the angle between the lines whose direction cosines are given by : 2l-m+2n=0, mn+nl+lm=0 .

Find the angle between the lines whose direction cosines are given by the equations: 2l-m+2n=0 mn+nl+lm=0.

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