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  2. Orthoptic (geometry) - Wikipedia

    en.wikipedia.org/wiki/Orthoptic_(geometry)

    The free term of a reduced quadratic equation is always the product of its solutions. Hence, if the tangents meet at (x 0, y 0) orthogonally, the following equations hold: = = The last equation is equivalent to =, which is the equation of the directrix.

  3. Ellipse - Wikipedia

    en.wikipedia.org/wiki/Ellipse

    An ellipse (red) obtained as the intersection of a cone with an inclined plane. Ellipse: notations Ellipses: examples with increasing eccentricity. In mathematics, an ellipse is a plane curve surrounding two focal points, such that for all points on the curve, the sum of the two distances to the focal points is a constant.

  4. Eccentricity (mathematics) - Wikipedia

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

    A family of conic sections of varying eccentricity share a focus point F and directrix line L, 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 ...

  5. Hyperbola - Wikipedia

    en.wikipedia.org/wiki/Hyperbola

    The directrix has equation =. With = (,), the ... This is the equation of an ellipse ... The normal line to the hyperbola at the same point is given by the equation ...

  6. Ruled surface - Wikipedia

    en.wikipedia.org/wiki/Ruled_surface

    Ruled surface generated by two Bézier curves as directrices (red, green). A surface in 3-dimensional Euclidean space is called a ruled surface if it is the union of a differentiable one-parameter family of lines.

  7. 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 ...

  8. File:Ellipse Properties of Directrix and String Construction.svg

    en.wikipedia.org/wiki/File:Ellipse_Properties_of...

    *The distance from a point, P, on the ellipse to a focus is always proportional to the distance to a vertical line, D, called the directrix. The constant of proportionality is the eccentricity, e. *The eccentricity is always between 0 and 1. At zero, the ellispe becomes a circle, at 1 the ellipse becomes a parabola. Greater than one, it is a ...

  9. Locus (mathematics) - Wikipedia

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

    Parabola: the set of points equidistant from a fixed point (the focus) and a line (the directrix). Hyperbola: the set of points for each of which the absolute value of the difference between the distances to two given foci is a constant. Ellipse: the set of points for each of which the sum of the distances to two given foci is a constant