= Theorem 73. The area of a parallelogram is the product of its base and its height: Area bh. A more general kind of quadrilateral is a trapezoid, that is, a quadrilateral in which two opposite sides are parallel. Let b and b' be the lengths of the two parallel sides of a trapezoid DABC D as shown in Figure 3.6. Again using Theorem 63, we define the height of OABCD to be the constant distance h between the parallel sides. See if you can find the area of the trapezoid by dividing it into closed regions whose areas you already know, and then applying Axiom 6(iii).