Smart, Edward Howard · London : Macmillian and Co. · leaf 190
ry. Cor. ST cuts the conic at the point of contact of thetangent from L. We have therefore The portion of a tangent intercepted between the curveand the directrix subtends a right angle at the focus. This also follows from the fact that the polar of a point onthe directrix passes through the focus.… … Fig. 83. Taking the figure (83) for the ellipse, we have, by the lastcorollary, PSF is a right angle. TANGENT AND NORMAL PROPERTIES 163 Let PG be the normal at P, and KF the directrix correspond-ing to S. Then angle SPG = angle SFP, each being complementary to SPF, = angle SKP, since SFKP is…
Geometry, Projective
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