Inner quadrilateral EFGH is formed by connecting the vertices of outer parallelogram ABCD with the midpoints of the opposite sides. Note that the diagonals are non-overlapping. This construction forms four “corner” triangles.
When α is zero, the original quadrilateral is show. When the corner triangles have been rotated 180°, a total of five congruent quadrilaterals are formed. The ratio of the inner quadrilateral to the outer quadrilateral is 1:5.