
ABCD and ABEF are two parallelograms on the same base AB and between the same parallels AB, DE
area (ABCD) = area (ABEF)

An alternate way of proving this theorem is as follows:
Since both parallelograms are between the same parallels, they are of equal heights. Also they have equal bases because the base is common; by formula,area of a parallelogram = base x height
they are of equal areas.

