单词	ellipse
释义	ellipse A conic formed by the intersection of a plane with a right circular cone, so that the plane is inclined to the axis of the cone at an angle in excess of half the apex angle of the cone. The ellipse has two vertices, which are joined by a line called the major axis . The centre of the ellipse falls on this line, midway between the vertices. The minor axis is the line perpendicular to the major axis that passes through the centre and joins two points on the ellipse. The foci of an ellipse are two points on the major axis so placed that for any point on the ellipse the sum of the distances from that point to each focus is constant. (See illustration.) The area of an ellipse is πab, where a and b are half the major and minor axes, respectively. For an ellipse centred at the origin, the equation in Cartesian coordinates is x2/a2 + y2/b2 = 1. The foci are at (ea, 0) and (-ea, 0), where e is the eccentricity. Each of the two chords of the ellipse passing through a focus and parallel to the minor axis is called a latus rectum and has a length equal to 2b2/a. An ellipse
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