Trapezoid

A trapezoid, also called a trapezium in some countries, is a quadrilateral with exactly one pair of parallel sides.

The parallel sides are called the bases and the non-parallel sides are the legs of the trapezoid.

An isosceles trapezoid is a trapezoid in which the two non-parallel sides are congruent.

The area A of a trapezoid is given by

where b₁ and b₂ are the lengths of the two parallel sides, and h is the height, as shown in the figure below.