Analytic geometry, for technical schools and colleges (1897)
Lambert, Preston Albert, 1862-1925 · New York, Macmillan · leaf 133
reflection proceed in parallel lines. It is this property of conic sections that suggested the term focus or burning point. 118 ANAL YTIC GEOMETR Y off an arc. In the parabola the parallels to the axis through the inter-sections of this circle with the directrix determine the points of tan-gency.… … Lines joining the second focus with the points of intersection of the twoarcs determine the points of tangency. In the ellipse TF + TF = 2 a,and by construction TF + TD = 2 a, hence TF - TD. The trian-gles TPF, TPD are equal, and PT is tangent to the ellipse. Inthe hyperbola TF - TF = 2a, TF - TD =…
Geometry, Analytic
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