MathDB
The angles COQ and DOQ are equal

Source: BMO Shortlist 2011, Bulgaria

April 9, 2012
geometrypower of a pointradical axisgeometry proposed

Problem Statement

Let ABCDABCD be a convex quadrangle such that AB=AC=BDAB=AC=BD (vertices are labelled in circular order). The lines ACAC and BDBD meet at point OO, the circles ABCABC and ADOADO meet again at point PP, and the lines APAP and BCBC meet at the point QQ. Show that the angles COQCOQ and DOQDOQ are equal.
Back to ProblemsView on AoPS