An elementary treatise on coordinate geometry of three dimensions (1912)
Bell, Robert J. T. (Robert John Tainsh), 1877-1963 · London : Macmillan and co., limited · leaf 166
res of a series of parallel plain;sections of a conicoid lie upon a diameter of the conicoid and the tangent plane at an extremity of the diameter idparallel to the plane sections. If, therefore, P and P (fig. 4-0)are the extremities of the diameter which passes throughthe centres of a system of… … Pig. 40. radius is called an umbilic. It is evident from the formof the hyperboloid of one sheet that the smallest closedsection is the principal elliptic section and that the surfacehas therefore no real umbilics. To find the umbilics of the ellipsoid -i + T2 + -2=l- If P, (£ )], £) is an umbilic,…
Geometry, Analytic
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