Grégoire Nicollier, Area of the orthic quadrilaterals of a convex cyclic orthodiagonal quadrilateral,
Forum Geometricorum, 16 (2016) 233--239.

Abstract. Among all orthic quadrilaterals inscribed in a given convex cyclic orthodiagonal quadrilateral, the orthic quadrilateral of the side midpoint rectangle has the largest area. We give here a short and simple proof of this recently established fact by describing the orthic quadrilaterals, inscribed or not, as a symmetric difference of orthic triangles and computing their area.

[ps file] [pdf]