1911 Encyclopædia Britannica/Trisectrix
TRISECTRIX, a curve which is a variety of the limaçon (q.v.) of Pascal, and named from its property of trisecting an angle. The polar equation is and the form of the curve is shown in the figure. To trisect an angle by means of this curve, describe a circle with centre O and radius OE, and let the given angle which is to be trisected be laid off from OE and cut the circle at S; let the chord ES cut the trisectrix in J. Then OJ trisects the given angle.