The proof is in the following form: Column 1 of proof; Column 2 of proof. Thus, we have: 1. The shape is a trapezoid; given 2. A line drawn through the transversal is parallel to the two sides of the trapezoid; given 3. The diagonals are divided proportionally; If three parallel lines happen to be cut by a common pair of transversals (lines that intersect them), then the transversal is proportionally divided.