1- Let be a quadrilateral, be a point on the plane. If then have a isogonal conjugates of . (and some result another)
http://www.geogebratube.org/student/m81105
2- If and then center of Pedal circles is Midpoints of two midpoint of diagonals
3-If and , is midpoint of , meets at . Then (a generalization Brahmagupta's theorem)
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