MtfceUanea Curio fa. 99 



the Coefficient of the third Term ^ bb]-ap 7 

 gives — ~ + I />, in the room of i j or C D 



2d 



in Carte fim\ ConftrufKon *, and from half 

 the Coefficient of the fourth Term is made 

 bp 



- i inftead of \ q or DE, and fo the 



Center of the Circle fought is determined. 

 Alfo becaufe one of the Roots of the nevv 

 Equation, viz.. ^rb is given, a point in the 

 Circumference will be given too, and confe- 

 quently the Radius. Laftly, Having de- 

 fcrib'd the Circle, Perpendiculars let fall 

 from its Interfedions with the Parabola, to 

 the Axis, will give the Roots of the Equa- 

 tion, both Affirmative and Negative, in the 

 fame manner as before. 



Now the Center of the Circle is found by 

 a mo ft eafy Conftru&ion, and which is to be 

 preferred to all others, in Cubick Equati- 

 ons. 



Fig. 11. Let A be the Vertex, and AF the 

 Axis of the defcrib'd Parabola AMD ; at a 

 diftance equal to b let DK be drawn parallel 

 to the Axis, to the Right Hand if it be -\-b 

 in the Equation, and to the Left, if it be 

 —b \ which Line fuppofe to meet the Para- 

 bola in the point D. Upon the Centers D 

 and A, and with equal R.adij, defcribe on 

 both fides two occult Arches, interfe&ing 

 one another, and thro' thofe points of In- 

 terferon draw the interminate Line BC 

 which cuts the imaginary Line AD in the 

 middle and at right Angles, and meets the 

 H % Axis 



