MathDB
Circle tangents

Source: Canada 1974/5

January 13, 2007
projective geometry

Problem Statement

Given a circle with diameter ABAB and a point XX on the circle different from AA and BB, let tat_{a}, tbt_{b} and txt_{x} be the tangents to the circle at AA, BB and XX respectively. Let ZZ be the point where line AXAX meets tbt_{b} and YY the point where line BXBX meets tat_{a}. Show that the three lines YZYZ, txt_{x} and ABAB are either concurrent (i.e., all pass through the same point) or parallel. 6762