The direction ratios of two lines are given bya+b+c=0 and ab+bc−2ca=0 . Then the angle between the lines is

Suppose that n=1Hence, the equations become a+b=1 and ab−b+2a=0Substitute b=1−a in the equationab−b+2a=0  and then solve for aIt implies that l=2±3 and l=2±3Therefore, the direction ratios are 2+3,−1−3,−1,2−3,−1+3,−1Suppose that θbe the angle between the lines whose direction ratios are  2+3,−1−3,−1,2−3,−1+3,−1Hence, cosθ=4−3+1−3+12+32+−1−32+1⋅2−32+−1+32+1=0Therefore, the measure of angle θ isπ2