Given planes are 2x + y – 2z = 5 and 3x – 6y – 2z = 7

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 = – 2

a₂ = 3, b₂ = – 6, c₂ = – 2

Hence, the angle between planes 2x + y – 2z = 5 and 3x – 6y – 2z = 7 is