x = ~, which is the directrix. Hence the directrix is the locus of the intersection oftangents at the extremities of focal chords. 79. In the ellipse any focal chord is at right anglesto the line joining its pole to the focus. Let QR be any focal chord; and let T on thedirectrix (§ 78, Cor. 2) be… … Also the equation of TF, through (ae, 0), (-,/?] is X - ae ae ¥ or aex --y = a^-¥; .... (2) and equations (1) and (2) evidently represent two linesat right angles to each other (§ 25). 80. In the ellipse if Q (.^, 2/) lies on the polar ofP{x, 2/), then P lies on the polar of Q. 156 Analytical…
Geometry, Analytic
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