6 Gee AND Adamson, Trisecting an Angle. 



Let ABC {Fig. 4) be the angle /3 to be trisected. With 

 B as centre and any radius BA describe a circle. Through 

 A draw any straight line cutting CB at R. Join AR. 

 On AR mark off RS equal to BA. -Then the locus of 

 vS is the conchoid required, and E, its intersection with 

 the circle, is the point through which A ED must be 

 drawn in order that the angle ADB, or a, shall be one- 

 third of the angle ABC. 



Pappus showed that any angle ABC {Figs. 5 and 6) 



Fig. 5. Method of Pappus (Use of Conchoid). 



could be trisected by solving the following vevais : 

 Through B draw BG perpendicular to BC, and through 



