Varignon
and Wittenbauer Parallelograms. Level: High School, SAT Prep, College
geometry.

Varignon parallelogram: The
figure formed when the midpoints of the sides of any quadrilateral
are joined in order is a parallelogram.

Wittenbauer parallelogram: If
the trisectors of each side of a quadrilateral are found, the
figure formed by connecting and extending adjacent points on
either side of a vertex is a parallelogram.