one pair of parallel sides – a trapezium (τραπέζιον), divided into isosceles (equal legs) and scalene (unequal) trapezia.Two types of trapezia were introduced by Proclus (412 to 485 AD) in his commentary on the first book of Euclid's Elements: The metric formulas in this article apply in convex trapezoids.Įtymology and trapezium versus trapezoid Hutton’s mistake in 1795 Īncient Greek mathematician Euclid defined five types of quadrilateral, of which four had two sets of parallel sides (known in English as square, rectangle, rhombus and rhomboid) and the last did not have two sets of parallel sides – a τραπέζια ( trapezia literally "a table", itself from τετράς ( tetrás), "four" + πέζα ( péza), "a foot end, border, edge"). If ABCD is a convex trapezoid, then ABDC is a concave trapezoid. A scalene trapezoid is a trapezoid with no sides of equal measure, in contrast with the special cases below.Ī trapezoid is usually considered to be a convex quadrilateral in Euclidean geometry, but there are also concave cases. The other two sides are called the legs (or the lateral sides) if they are not parallel otherwise, the trapezoid is a parallelogram, and there are two pairs of bases. The parallel sides are called the bases of the trapezoid. In geometry, a trapezoid ( / ˈ t r æ p ə z ɔɪ d/) in USA and Canadian English, or trapezium ( / t r ə ˈ p iː z i ə m/) in British and other forms of English, is a quadrilateral that has at least one pair of parallel sides. Look up trapezoid in Wiktionary, the free dictionary.
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