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Barbier's theorem : ウィキペディア英語版 | Barbier's theorem
In geometry, Barbier's theorem states that every curve of constant width has perimeter π times its width, regardless of its precise shape.〔.〕 This theorem was first published by Joseph-Émile Barbier in 1860.〔. See in particular pp. 283–285.〕 ==Examples== The most familiar examples of curves of constant width are the circle and the Reuleaux triangle. For a circle, the width is the same as the diameter; a circle of width ''w'' has perimeter π''w''. A Reuleaux triangle of width ''w'' consists of three arcs of circles of radius ''w''. Each of these arcs has central angle π/3, so the perimeter of the Reuleaux triangle of width ''w'' is equal to half the perimeter of a circle of radius ''w'' and therefore is equal to π''w''. A similar analysis of other simple examples such as Reuleaux polygons gives the same answer.
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「Barbier's theorem」の詳細全文を読む
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