MathDB
Chisinau MO p132 1976 X AB/CD = AO x BO / CO x DO in tangential ABCD

Source:

March 16, 2021
geometryratiotangential

Problem Statement

Let OO be the center of a circle inscribed in a convex quadrilateral ABCDABCD and AB=a|AB|= a, CD=|CD|=c. Prove that ac=AOBOCODO.\frac{a}{c}=\frac{AO\cdot BO}{CO\cdot DO}.