A trapezoid has only one pair of opposite sides that are parallel to one another. The parallel sides are referred to as bases, and the nonparallel sides are called legs.
A trapezoid with legs of equal length is called an isosceles trapezoid. This type of trapezoid displays additional geometric properties compared to a normal trapezoid.
There are four angles within a trapezoid defined by the sides that connect to form them. Two adjacent angles that share one leg of a trapezoid are called supplementary angles. By definition, two supplementary angles add up to 180 degrees for all trapezoids. In addition, the two angles formed from the base of an isosceles trapezoid, or base angles, will always be congruent.
Two diagonals connect opposite corners within a trapezoid. Diagonals are often used for finding the measure and length of unknown angles and sides using various geometric theorems and calculations. In an isosceles trapezoid, the two diagonals are equivalent in length.
The median line, or midsegment, of a trapezoid connects the midpoints of the two legs (nonparallel sides) and is parallel to the bases (parallel sides). The length of the median line is equal to the average length of the two bases. The calculation of the median is also used for determining the area of a trapezoid, which is defined as the height multiplied by the average length of the two bases, or median. Use the following formula:
Area of trapezoid = height x (sum of base lengths/2)