- P = perimeter
- a,b,c,d are the sides of the Trapezium
- Thes sides a,b are parallels (a//b)
In Euclidean geometry, a convex quadrilateral with at least one pair of parallel sides is referred to as a trapezoid but as a trapezium in English outside North America. The parallel sides (a//b) are called the bases of the trapezoid and the other two sides are called the legs or the lateral sides (if they are not parallel; otherwise there are two pairs of bases).