Given that the space quadrilateral ABCD E F G is the midpoint of AB BC CD ad respectively, we prove the efgh parallelogram

Given that the space quadrilateral ABCD E F G is the midpoint of AB BC CD ad respectively, we prove the efgh parallelogram

Connect AC and BD
So eh / / BD
The same is true for FG / / BD
So eh / / FG
Similarly, EF / / GH
The two pairs of variables are parallel to each other, so efgh is positive for the parallelogram