Русский: Эллипс как коническое сечение и шары Данделена. Показаны фокусы эллипса (две точки) и его директрисы (синие линии). — эксцентриситет эллипса, — угол между секущей плоскостью и осью конуса.
English: Ellipse as the conic section and Dandelin spheres. Foci of the ellipse are shown as two dots, directrices are blue lines. — eccentricity of the ellipse, — angle between the secant plane and the axis of the cone.
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