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In Euclidean geometry, a convex quadrilateral wi at least ane pair o parallel sides is referred tae as a trapezoid in American Inglis an as a trapezium in Inglis ootside North Americae. The parallel sides are cried the bases o the trapezoid an the ither twa sides are cried the legs or the lateral sides (if thay are nae parallel; itherwise thare are twa pairs o bases). A scalene trapezoid is a trapezoid wi na sides o equal measure, in contrast tae some special cases. A trapezoid wi vertices ABCD is denoted ABCD.
Thare is some disagreement whether parallelograms, which hae twa pairs o parallel sides, should be coontit as trapezoids. Some define a trapezoid as a quadrilateral havin exactly ane pair o parallel sides (the exclusive defineetion), tharebi excludin parallelograms. Ithers define a trapezoid as a quadrilateral wi at least ane pair o parallel sides (the inclusive defineetion), makin the parallelogram a special type o trapezoid. The latter defineetion is consistent wi its uises in heicher mathematics such as calculus. The umwhile defineetion would mak such concepts as the trapezoidal approximation tae a definite integral ill-defined. This airticle uises the inclusive defineetion an considers parallelograms as special cases o a trapezoid. This is an aa advocated in the taxonomy o quadrilaterals.