The perpendicular distance from a point with position vector u̅ to the plane r̅.n̅ = p is

The perpendicular distance from a point ( x₁, y₁ ,z₁ ) to the plane ax + by +cz = p is

The perpendicular distance from the origin to the plane ax+ by+ cz+ d = 0 is

The distance between two parallel planes ax+by+cz+d₁ = 0 and ax+by+cz+d₂ = 0 is