MathDB
Infinite family of circles passing through a point

Source: Russian TST 2015, Day 7 P2

April 21, 2023
geometrycircles

Problem Statement

In the isosceles triangle ABCABC where AB=ACAB = AC, the point II{} is the center of the inscribed circle. Through the point AA{} all the rays lying inside the angle BACBAC are drawn. For each such ray, we denote by XX{} and YY{} the points of intersection with the arc BICBIC and the straight line BCBC respectively. The circle γ\gamma passing through XX{} and YY{}, which touches the arc BICBIC at the point XX{} is considered. Prove that all the circles γ\gamma pass through a fixed point.