# Trapezoid

convex quadrilateral with at least one pair of parallel sides

A trapezoid (in North America) or trapezium (in Britain and elsewhere) is a quadrilateral, which is defined as a shape with four sides. This shape has two parallel sides which are called the bases of the trapezoid, and another two sides called its legs. In North America, the term "trapezium" is used for what is elsewhere called an irregular quadrilateral, which has no parallel sides.[1]

## Special cases

Some trapezoids are special cases where they have at least one noteworthy feature:

• Isosceles trapezoids: These have legs that are of the same length, and because of that, this trapezoid has a pair of angles of the same wideness (congruent).
• Parallelogramsː This is a trapezoid where two pairs of its sides are parallel to each other. As a result, there are two pairs of vertices in a parallelogram that are congruent.
• Tangential trapezoidsː These are trapezoids whose sides can be tangent to a circle placed inside of them, to which the circle is called an incircle.

## Calculating area

To calculate the area of a trapezoid, you must add the two parallel sides together, divide that by 2, then times that by its height.

${\displaystyle A={\frac {a+b}{2}}\cdot h}$

## References

1. "1913 American definition of trapezium". Merriam-Webster Online Dictionary. Retrieved 2007-12-10.