when can a trapezoid also be called a parallelogram
Trapezoid There is some disagreement whether parallelograms, which have two pairs of parallel sides, should be regarded as trapezoids. Some define a trapezoid as a quadrilateral having only one pair of parallel sides (the exclusive definition), thereby excluding parallelograms.[6] Others[7] define a trapezoid as a quadrilateral with at least one pair of parallel sides (the inclusive definition[8]), making the parallelogram a special type of trapezoid. The latter definition is consistent with its uses in higher mathematics such as calculus. The former definition would make such concepts as the trapezoidal approximation to a definite integral ill-defined. This article uses the inclusive definition and considers parallelograms as special cases of a trapezoid. This is also advocated in the taxonomy of quadrilaterals.
National Hockey League rules New since the 2005–06 NHL season, after testing in the American Hockey League, a trapezoid is marked behind each goalie net. The goalie can only play the puck within that area or in front of the goal line. If he plays the puck behind the goal line and not in the trapezoid, a 2-minute minor penalty for delay of game will be assessed by the referees. This rule is widely referred to as the "Brodeur rule", after New Jersey Devils goalie Martin Brodeur, whose puckhandling behind the net is believed to be the cause for the rule.[2][3] In 2014, the NHL lengthened the goal-line side of the trapezoid by two feet on both sides of the net.[4]