II. The Invention of the Central Rule, in the Case of Fig. 11. and the like.
1. □HA=bb+dd as above.
2 Putting x for NO, as sought, we may infer from a new Property of the Parabola, which we have demonstrated Prop. 6. lib. 2
as L to NO so OR to AO, i. e. (putting a for BA or FO given; that NO−OF i. e. NF or OR shall be = x−a) as L to x so x−a to 〈 math 〉〈 math 〉 = AO.
Therefore having substracted AD i. e. b from AO, you'l have DO or HP = 〈 math 〉〈 math 〉; whose □ is