Varignon's theorem states that the figure formed when the midpoints of the sides of a convex quadrilateral are joined in order is a parallelogram. Equivalently, the bimedians bisect each other.
The area of the Varignon parallelogram of a convex quadrilateral is half that of the quadrilateral, and the perimeter is equal to the sum of the diagonals of the original quadrilateral.
The distinct theorem of the same name in mechanics is the principle of moments, which concerns the moments of forces rather than quadrilaterals.
