o theplane of the paper POQ. Forthe tangent plane at Q passesthrough PQ and is perpendicular to the plane of the paper;the tangent line to the section QOR lies in the tangent plane,and is therefore also perpendicular to the plane of the paper.Since then 0^ is perpendicular to the tangent line in… … 456 SURFACES DERIVED FROM QUADRICS. 491. The perpendicular to the tangent plane to the apstdalsurface at T lies also in the plane POQ, and is perpendicularand equal to OPf^ Consider first a radius OT of the apsidal surface, inde-finitely near to OT^ and lying in the plane TOR^ perpendicularto the…
Geometry, Analytic · Surfaces
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