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A trapezoid is a quadrilateral with exactly one pair of parallel sides. The parallel sides are called the bases of the trapezoid, and the two other sides are called the legs. Two angles that have a base as a common side are called the base angles.
If the legs are equal in length, the shape is known as an isosceles trapezoid.
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Inclusive Definition |
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A trapezoid is a quadrilateral with at least one pair of parallel sides. |
By this definition, parallelograms are a special type of trapezoid. However, unless otherwise stated, when working with trapezoids, the exclusive definition is the one to be used.
The term trapezium has different meanings in British and American English.
| Trapezium | |
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| British English | A quadrilateral with a pair of parallel sides |
| American English | A quadrilateral with no parallel sides |
The British definition of a trapezium is the same as the definition of a trapezoid in American English. On the other hand, a quadrilateral with no parallel sides is now called an irregular quadrilateral in British English, but in the past it was confusingly called a trapezoid.
