Distance = √((x₂−x₁)² + (y₂−y₁)²). The Euclidean distance formula for 2D coordinates.
Points (0,0) and (3,4): distance = √(9+16) = √25 = 5.
3D distance: √((x₂−x₁)² + (y₂−y₁)² + (z₂−z₁)²).
d = √((x₂−x₁)² + (y₂−y₁)²). The straight-line distance between two points on a plane.