- Cartesian equation:
- or parametrically:
DescriptionThe straight line must be one of the earliest curves studied, but Euclid in his Elementsalthough he devotes much study to the straight line, does not consider it a curve.
In fact nobody attempted a general definition of a curve until Jordan in his Cours d'Analysein 1893.
The inverse of a straight line is a circle if the centre of inversion is not on the line.
The negative pedal of the straight line is a parabola if the pedal point is not on the line.
Since normals to a straight line never intersect and tangents coincide with the curve, evolutes, involutes and pedal curves are not too interesting.
Other Web site:
Jeff Miller (Why is the slope of a straight line called ?)