Given planes are 2x – 3y + 4z = 1 and – x + y = 4

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 = – 3, c₁ = 4

a₂ = – 1, b₂ = 1, c₂ = 0

Hence, the angle between planes 2x – 3y + 4z = 1 and – x + y = 4 is