The correct answer is Option (2) → 45°
→n1 ⊥ plane 1 = 4ˆi+8ˆj+ˆk
→n2 ⊥ plane 2 = ˆj+ˆk
angle between planes = angle between normals
\vec{n_1}.\vec{n_2}=|\vec{n_1}||\vec{n_2}|\cos θ
9=\sqrt{4^2+8^2+1}\sqrt{1^2+1^2}\cos θ
\cos θ=\frac{1}{\sqrt{2}}
θ=45° |