Rational trigonometry is a parallel system of trigonometry (developed by my supervisor, Norman Wildberger), congruent to standard Euclidean geometry in many ways. The two fundamental quantities of rational trigonometry are:

- Quadrance as the relationship between points
- Spread as the relationship between lines

Rational trigonometry is defined on the Cartesian plane, so:

- A point is defined by an ordered pair: [x,y]
- A line is defined by a linear equation: ax + by + c = 0