Definition:Complements of Parallelograms

Definition

Let $ABDC$ and $EFHG$ be two parallelograms with the same angles, which share a diagonal, such that $ABDC \cap EFHG \ne \O$.

Then the two parallelograms $CIGK$ and $BJHL$ are known as the complements of the parallelograms $ABDC$ and $EFHG$.

Linguistic Note

The word complement comes from the idea of complete-ment, it being the thing needed to complete something else.

It is a common mistake to confuse the words complement and compliment. Usually the latter is mistakenly used when the former is meant.

In this context, the thing being completed is the large parallelogram $AIJF$.