An elementary treatise on analytical geometry : embracing plane co-ordinate geometry, and an introduction to geometry of three dimensions (1869)
Johnson, William Woolsey, 1841-1927 · Philadelphia : J.B. Lippincott · leaf 189
ess theperpendiculars in terms of theco-ordinates of Pv Therefore, using the equation A2YYl — B2XXX + A2B2 =- 0 for the tangent, and the method of Art. 73 for the perpendicularfrom any point, we have for the foci F, (Ae, 0) and F, (— Ae, 0), gD = -Ag(eX1-A) ^ F3y=AB(eXI + A)^X/A4YX2 + B4XX2… … TANGENT AND FOCAL LINES. 185 therefore the angles FPjD and FPjD are equal. A similar proofmay be used in the case of the ellipse. 252. It has been proved, in Art. 245. that the product of theperpendiculars FD and FD is numerically equal to B2, and in Art.248, that the product of the focal distances…
Geometry, Analytic
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