MathDB
AT bisects BC

Source: 2021 China Second Round A2 , additional test, p1

April 29, 2024
geometrybisects segment

Problem Statement

As shown in the figure, in the acute angle ABC\vartriangle ABC, AB>ACAB > AC, MM is the midpoint of the minor arc BCBC of the circumcircle Ω\Omega of ABC\vartriangle ABC. KK is the intersection point of the bisector of the exterior angle BAC\angle BAC and the extension line of BCBC. From point AA draw a line perpendicular on BCBC and take a point DD (different from AA) on that line , such that DM=AMDM = AM. Let the circumscribed circle of ADK\vartriangle ADK intersect the circle Ω\Omega at point AA and at another point TT. Prove that ATAT bisects line segment BCBC. https://cdn.artofproblemsolving.com/attachments/1/3/6fde30405101620828d63ae31b8c0ffcec972f.png