English: Changing ellipse, then hyperbola, when eccentricity e changes and a (semi-major axis for ellipse and the distance from the center to the tops for hyperbola) remains constant (equal to 3). Directrices are in magenta, hyperbola's asymptotes are in light blue, and foci are solid blue dots.
Русский: Эллипс и гипербола при постоянном параметре a и меняющемся эксцентриситете e.