We know, the angle between two planes,

a₁x + b₁y + c₁z + d₁=0 and a₂x + b₂y + c₂z + d₂=0 is,

Here, a₁=2, b₁= - 1, c₁=1, d₁= - 6 and a₂=1, b₂=1, c₂=2,

d₂= - 3.

So, the acute angle between the planes 2x–y + z=6 and

x + y + 2z = 3 is

θ=60 ̊

the acute angle between the planes 2x–y + z=6 and

x + y + 2z = 3 is 60 ̊.