Problem

Source: 2-nd Taiwanese Mathematical Olympiad 1993

Tags: geometry, parallelogram, symmetry, power of a point, radical axis, geometry unsolved



Let $E$ and $F$ are distinct points on the diagonal $AC$ of a parallelogram $ABCD$ . Prove that , if there exists a cricle through $E,F$ tangent to rays $BA,BC$ then there also exists a cricle through $E,F$ tangent to rays $DA,DC$.