Second Droz-Farny Circle
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Let ABC be a triangle. Draw the circles about the midpoints of AB, AC, and BC that pass through the orthocenter (the point of intersection of the triangle's altitudes). These three circles intersect the sides of ABC or their extensions in six points. Then those points lie on a circle (the second Droz-Farny circle).
Contributed by: Jay Warendorff (March 2011)
Open content licensed under CC BY-NC-SA