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A pentagram (sometimes known as a pentalpha or pentangle or a star pentagon) is the shape of a five-pointed star drawn with five straight strokes. The word ''pentagram'' comes from the Greek word πεντάγραμμον (''pentagrammon''),〔(πεντάγραμμον ), Henry George Liddell, Robert Scott, ''A Greek-English Lexicon'', on Perseus; a noun form of adjectival πεντάγραμμος (''pentagrammos'') or πεντέγραμμος (''pentegrammos''), a word meaning roughly "five-lined" or "five lines"〕 from πέντε (''pente''), "five" + γραμμή (''grammē''), "line".〔(πέντε ), Henry George Liddell, Robert Scott, ''A Greek-English Lexicon'', on Perseus; (γραμμή ), Henry George Liddell, Robert Scott, ''A Greek-English Lexicon'', on Perseus〕 The word "pentacle" is sometimes used synonymously with "pentagram"〔this usage is borne out by the Oxford English Dictionary, although that work specifies that a circumscription makes the shape more particularly a pentacle. "Pentacle", ''Oxford English Dictionary'': "Middle French ''pentacle'' talisman (1555, in English from 1561 ), most often in the form of a five-pointed star and its etymon post-classical Latin ''pentaculum '' () A pentagram, esp. one enclosed in a circle; a talisman or magical symbol in the shape of or inscribed with a pentagram. Also, in extended use: any similar magical symbol (freq. applied to a hexagram formed by two intersecting or interlaced equilateral triangles)."〕 The word ''pentalpha'' is a learned modern (17th-century) revival of a post-classical Greek name of the shape.〔πένταλϕα, "five Alphas", interpreting the shape as five Α shapes overlapping at 72-degree angles.〕 ==Geometry== The pentagram is the simplest regular star polygon. The pentagram contains ten points (the five points of the star, and the five vertices of the inner pentagon) and fifteen line segments. It is represented by the Schläfli symbol . Like a regular pentagon, and a regular pentagon with a pentagram constructed inside it, the regular pentagram has as its symmetry group the dihedral group of order 10. ===Construction=== The pentagram can be constructed by connecting alternate vertices of a pentagon; see details of the construction. It can also be constructed as a stellation of a pentagon, by extending the edges of a pentagon until the lines intersect. 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「Pentagram」の詳細全文を読む スポンサード リンク
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