Two-point formulas
Distance = √((x₂−x₁)²+(y₂−y₁)²) · Midpoint = ((x₁+x₂)/2, (y₁+y₂)/2) · Slope = (y₂−y₁)/(x₂−x₁)
Vertical and horizontal lines
A vertical line has undefined slope and equation x = constant. A horizontal line has slope zero.
Three-point triangle
Adding point C calculates triangle area by the coordinate determinant, perimeter from three distances and centroid by averaging the coordinates.