conic section

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Eccentricity of conic sectionsThe eccentricity of a conic section completely characterizes its shape. For example, all circles have zero eccentricity, and all parabolas have unit eccentricity; hence, all circles (and all parabolas) have the same shape, only varying in size. (Under appropriate magnification they are indistinguishable.) In contrast, ellipses and hyperbolas vary greatly in shape.

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Projective conic sectionsThe conic sections (ellipse, parabola, and hyperbola) can be generated by projecting the circle formed by the intersection of a cone with a plane (the reality plane, or RP) perpendicular to the cone's central axis. The image of the circle is projected onto a plane (the projective plane, or PP) that is oriented at the same angle as the cutting plane (Ω) passing through the apex (“eye”) of the double cone. In this example, the orientation of Ω produces an ellipse in PP.

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Also Known As	conic

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Eccentricity of conic sectionsThe eccentricity of a conic section completely characterizes its shape. For example, all circles have zero eccentricity, and all parabolas have unit eccentricity; hence, all circles (and all parabolas) have the same shape, only varying in size. (Under appropriate magnification they are indistinguishable.) In contrast, ellipses and hyperbolas vary greatly in shape.

Parabolic satellite dish antenna

Projective conic sectionsThe conic sections (ellipse, parabola, and hyperbola) can be generated by projecting the circle formed by the intersection of a cone with a plane (the reality plane, or RP) perpendicular to the cone's central axis. The image of the circle is projected onto a plane (the projective plane, or PP) that is oriented at the same angle as the cutting plane (Ω) passing through the apex (“eye”) of the double cone. In this example, the orientation of Ω produces an ellipse in PP.

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Topics

ellipse hyperbola parabola circle directrix eccentricity focus latus rectum great circle arc catenary spiral Lissajous figure rhumb line involute brachistochrone curvature orthogonal trajectory tangent slope

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projective geometry: Projective conic sections

Key People

Blaise Pascal

Blaise Pascal

French philosopher and scientist

Apollonius of Perga

Greek mathematician

Girard Desargues

French mathematician

Colin Maclaurin, engraving by S. Freeman; in the British Museum.

Colin Maclaurin

Scottish mathematician

Conon of Samos

Greek mathematician

Charles-Julien Brianchon

French mathematician

Menaechmus

Greek mathematician

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Equations written on blackboard

Numbers and Mathematics