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In geometry, the semi-minor axis (also semiminor axis) is a line segment associated with most conic sections (that is, with ellipses and hyperbolas) that is at right angles with the semi-major axis and has one end at the center of the conic section. It is one of the axes of symmetry for the curve: in an ellipse, the shorter one; in a hyperbola, the one that does not intersect the hyperbola. ==Ellipse== 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 semi-minor axis ''b'' is related to the semi-major axis through the eccentricity and the semi-latus rectum , as follows: : :. The semi-minor axis of an ellipse is the geometric mean of the maximum and minimum distances and of the ellipse from a focus — that is, of the distances from a focus to the endpoints of the major axis: : A parabola can be obtained as the limit of a sequence of ellipses where one focus is kept fixed as the other is allowed to move arbitrarily far away in one direction, keeping ''l'' fixed. Thus ''a'' and ''b'' tend to infinity, ''a'' faster than ''b''. The length of the semi-minor axis could also be found using the following formula,〔http://www.mathopenref.com/ellipseaxes.html,"Major / Minor axis of an ellipse",Math Open Reference, 12 May 2013〕 : where f is the distance between the foci, p and q are the distances from each focus to any point in the ellipse. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Semi-minor axis」の詳細全文を読む スポンサード リンク
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