MathDB
harrrrrd quadrilateral property

Source: ARO 2008

June 11, 2008
geometrygeometric transformationdilationangle bisector

Problem Statement

In convex quadrilateral ABCD ABCD, the rays BA,CD BA,CD meet at P P, and the rays BC,AD BC,AD meet at Q Q. H H is the projection of D D on PQ PQ. Prove that there is a circle inscribed in ABCD ABCD if and only if the incircles of triangles ADP,CDQ ADP,CDQ are visible from H H under the same angle.
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