erefore the present theoremfollows at once from Art. 249. We get an expression for the sum or difference of the angles,in terms of the given axis, by considering the principal sec-tion containing the greatest and least axes of the quadric.We obtain the cyclic planes by inflecting in that… … a cos a sin a —^ + —^c a But a is obviously an axis of the section which passesthrough it and is perpendicular to the plane of the figure,and (if a be greater than h) a is evidently half the sum ofthe angles BOA\ B OA which the plane of the section makeswith the cyclic planes. If a be less than 5,…
Geometry, Analytic · Surfaces
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