Given planes are 2x – y + z = 4 and x + y + 2z = 3

We know that angle between two planes,

a₁x + b₁y + c₁z + d₁ = 0

a₂x + b₂y + c₂z + d₂ = 0 is given as

Here we have,

a₁ = 2, b₁ = – 1, c₁ = 1

a₂ = 1, b₂ = 1, c₂ = 2

Hence, the angle between planes 2x – y + z = 4 and x + y + 2z = 3 is .