[2] Note that a non-rectangular parallelogram is not an isosceles trapezoid because of the second condition, or because it has no line of symmetry.

Rectangles and squares are usually considered to be special cases of isosceles trapezoids though some sources would exclude them.

They can also be seen dissected from regular polygons of 5 sides or more as a truncation of 4 sequential vertices.

Any non-self-crossing quadrilateral with exactly one axis of symmetry must be either an isosceles trapezoid or a kite.

The area of an isosceles (or any) trapezoid is equal to the average of the lengths of the base and top (the parallel sides) times the height.

In the adjacent diagram, if we write AD = a, and BC = b, and the height h is the length of a line segment between AD and BC that is perpendicular to them, then the area K is If instead of the height of the trapezoid, the common length of the legs AB =CD = c is known, then the area can be computed using Brahmagupta's formula for the area of a cyclic quadrilateral, which with two sides equal simplifies to where

The previous formula for area can also be written as The radius in the circumscribed circle is given by[7] In a rectangle where a = b this is simplified to