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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 ...
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.
A conic is defined as the locus of points for each of which the distance to the focus divided by the distance to the directrix is a fixed positive constant, called the eccentricity e. If 0 < e < 1 the conic is an ellipse, if e = 1 the conic is a parabola, and if e > 1 the conic is a hyperbola.
In geometry, the lemniscate of Bernoulli is a plane curve defined from two given points F 1 and F 2, known as foci, at distance 2c from each other as the locus of points P so that PF 1 ·PF 2 = c 2. The curve has a shape similar to the numeral 8 and to the ∞ symbol.
The semi-minor axis of an ellipse runs from the center of the ellipse (a point halfway between and on the line running between the foci) to the edge of the ellipse. The semi-minor axis is half of the minor axis. The minor axis is the longest line segment perpendicular to the major axis that connects two points on the ellipse's edge.
The coordinates (,) have a simple relation to the distances to the foci and . For any point in the plane, the sum d 1 + d 2 {\displaystyle d_{1}+d_{2}} of its distances to the foci equals 2 a σ {\displaystyle 2a\sigma } , whereas their difference d 1 − d 2 {\displaystyle d_{1}-d_{2}} equals 2 a τ {\displaystyle 2a\tau } .
Let f be the distance from the vertex V (on both the hyperbola and its axis through the two foci) to the nearer focus. Then the distance, along a line perpendicular to that axis, from that focus to a point P on the hyperbola is greater than 2f. The tangent to the hyperbola at P intersects that axis at point Q at an angle ∠PQV of greater than ...
The points of tangency F 1, F 2 are the foci of the blue ellipse. The spheres are also tangent to the cone at circles k 1, k 2. For a point P on the ellipse, the tangent segments PF 1 and PF 2 can each be reflected to other tangents of equal length, PF 1 = PP 1 and PF 2 = PP 2, with PP 1 and PP 2 colinear along the ray SP.