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Concept

Trapezoid

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.
Trapezoid
If the legs are equal in length, the shape is known as an isosceles trapezoid.

Extra

 Inclusive Definition of Trapezoids

The definition presented before is known as the exclusive definition. However, there is a second approach for how to define a trapezoid (US), or trapezium (UK). This difference stems from whether parallelograms should be regarded as trapezoids or not.

Inclusive Definition

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.

Trapezium: British vs American English

The term trapezium has different meanings in British and American English.

Trapezium
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.

Trapezoid vs Trapezium
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