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In geometry, a focaloid is a shell bounded by two concentric, confocal ellipses (in 2D) or ellipsoids (in 3D). When the thickness of the shell becomes negligible, it is called a thin focaloid. ==Mathematical definition (3D)== If one boundary surface is given by : with semiaxes ''a'', ''b'', ''c'' the second surface is given by : The thin focaloid is then given by the limit . In general, a focaloid could be understood as a shell consisting out of two closed coordinate surfaces of a confocal ellipsoidal coordinate system. 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「Focaloid」の詳細全文を読む スポンサード リンク
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