Mathematics - 3D-Coordinate Geometry Question with Solution | TestHub

If the direction ratios of two lines are given by $\left(a_1,b_1,c_1\right)$ and $\left(a_2,b_2,c_2\right)$ then the acute angle between the lines is ${\cos }^{-1}\frac{a_1{a}_2+b_1{b}_2+c_1{c}_2}{\sqrt{a_1^2+b_1^2+c_1^2}\sqrt{a_2^2+b_2^2+c_2^2}}$. If the direction ratios of two non parallel lines are connected by the relation $a+b+c=0$ and $2ab-bc+2ca=0$, then the angle between the lines is