There is a Building, which is tilted and equation of two different walls are $2x-y +z= 4 $ and $x+y +2z = 3.$ Angle between the walls is :

$\frac{\pi }{3}$

The correct answer is Option (2) → $\frac{\pi }{3}$

$\vec{n_1} ⊥ (Plane: 2x-y+z=4) = 2\hat i-\hat j+1\hat k$

$\vec{n_2} ⊥ (Plane: x+y+2z=3) =\hat i+\hat j+2\hat k$

Computing angles

$\vec{n_1}.\vec{n_2}=|\vec{n_1}||\vec{n_2}|\cos θ$

$\cos θ=\frac{2-1+2}{\sqrt{6}\sqrt{6}}=\frac{3}{\sqrt{6}×\sqrt{6}}=\frac{1}{2}⇒θ=\frac{\pi }{3}$