Definition

A coordinate plane is a plane whose points have been placed in one- to-one correspondence with the set of ordered pairs of real numbers, ℝ × ℝ.

Distance in a Coordiante Plane

The distance |P₁P₂| between the points P₁ and P₂ with coordinates (x₁, y₁) and (x₂, y₂) respectively is given by

Proof: ΔP₁TP₂ is right with m(∠T) = 90^o

(Distance formula between P₁ and P₂)