168 CONIC SECTIONS, PROP. VII. If from any point F in the ordinate PR- the line FQ isdrawn parallel to the axis and meeting the parabola in Q, then Draw QE perpendicular to theaxis; then because PR is dividedinto two equal parts in N and twounequal in F, .-. PF.FR = PN*- NF2 (Euclid,II. 5.) = PN* -…
