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  2. Directrix - Wikipedia

    en.wikipedia.org/wiki/Directrix

    Directrix is a spaceship in the Lensman series of novels by E. E. Smith. Directrix is the name of an alternative punk band in Chicago. Directrix - a feminine form of director in the context of grammatical gender

  3. Ruled surface - Wikipedia

    en.wikipedia.org/wiki/Ruled_surface

    The curve () is called the directrix of the representation. The directrix may collapse to a point (in case of a cone, see example below). The ruled surface above may alternatively be described by (,) = () + ()

  4. Generatrix - Wikipedia

    en.wikipedia.org/wiki/Generatrix

    A cone can be generated by moving a line (the generatrix) fixed at the future apex of the cone along a closed curve (the directrix); if that directrix is a circle perpendicular to the line connecting its center to the apex, the motion is rotation around a fixed axis and the resulting shape is a circular cone.

  5. Conical surface - Wikipedia

    en.wikipedia.org/wiki/Conical_surface

    The directrix is often taken as a plane curve, in a plane not containing the apex, but this is not a requirement. [1] In general, a conical surface consists of two congruent unbounded halves joined by the apex. Each half is called a nappe, and is the union of all the rays that start at the apex and pass through a point of some fixed space curve ...

  6. Parabola - Wikipedia

    en.wikipedia.org/wiki/Parabola

    In this diagram, F is the focus of the parabola, and T and U lie on its directrix. P is an arbitrary point on the parabola. PT is perpendicular to the directrix, and the line MP bisects angle ∠FPT. Q is another point on the parabola, with QU perpendicular to the directrix. We know that FP = PT and FQ = QU.

  7. Channel surface - Wikipedia

    en.wikipedia.org/wiki/Channel_surface

    canal surface: directrix is a helix, with its generating spheres pipe surface: directrix is a helix, with generating spheres pipe surface: directrix is a helix. In geometry and topology, a channel or canal surface is a surface formed as the envelope of a family of spheres whose centers lie on a space curve, its directrix.

  8. Eccentricity (mathematics) - Wikipedia

    en.wikipedia.org/wiki/Eccentricity_(mathematics)

    A family of conic sections of varying eccentricity share a focus point and directrix line, including an ellipse (red, e = 1/2), a parabola (green, e = 1), and a hyperbola (blue, e = 2). The conic of eccentricity 0 in this figure is an infinitesimal circle centered at the focus, and the conic of eccentricity ∞ is an infinitesimally separated ...

  9. Conoid - Wikipedia

    en.wikipedia.org/wiki/Conoid

    (1) All rulings are parallel to a plane, the directrix plane. (2) All rulings intersect a fixed line, the axis. The conoid is a right conoid if its axis is perpendicular to its directrix plane. Hence all rulings are perpendicular to the axis. Because of (1) any conoid is a Catalan surface and can be represented parametrically by