An orthodiagonal quadrangle is a quadrangle whose diagonals are perpendicular to each other. If , , , and are the sides of a quadrangle, then this quadrangle is orthodiagonal iff .

If is a cyclic orthodiagonal quadrangle, then the quadrangle formed by the tangents to the circumcircle through the vertices of form a bicentric quadrilateral . The circumcenters of and and the point of intersection of the diagonals of are collinear.

This entry contributed by Floor van Lamoen

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van Lamoen, Floor. "Orthodiagonal Quadrangle." From MathWorld--A Wolfram Web Resource, created by Eric W. Weisstein. https://mathworld.wolfram.com/OrthodiagonalQuadrangle.html