IN every problem in which it is asked to investigate a locus, be this on a straight line or on a curve, one arrives at an equation determining an arbitrarily chosen point on the required locus [1.1] if one considers as known and determinate two unknown and indeterminate line segments enclosing a given or chosen angle [1.2]. If in this equation (after reduction to its simplest form) neither of the two unknown quantities has been raised to the second or a higher power – that is, if they do not occur multiplied by themselves nor by each other – then the required locus will be a straight line. But if one of these unknown quantities has been raised to the second power but the other not and if this other one has not been multiplied by itself nor by the first one, then the required locus will be a parabola.

doi.org/10.1007/978-0-85729-142-4_3
Sources and Studies in the History of Mathematics and Physical Sciences
Centrum Wiskunde & Informatica, Amsterdam (CWI), The Netherlands

Grootendorst, A., Aarts, J., Bakker, M., & Erné, R. (2010). Latin text and translation. In Jan de Witt’s Elementa Curvarum Linearum (pp. 59–255). doi:10.1007/978-0-85729-142-4_3