MathDB
37th Austrian Mathematical Olympiad 2006

Source: round1, problem3 - triangles, cirumcircles and tangent lines

February 10, 2009
geometrycircumcircleangle bisectorexterior anglegeometry unsolved

Problem Statement

In a non isosceles triangle ABC ABC let w w be the angle bisector of the exterior angle at C C. Let D D be the point of intersection of w w with the extension of AB AB. Let kA k_A be the circumcircle of the triangle ADC ADC and analogy kB k_B the circumcircle of the triangle BDC BDC. Let tA t_A be the tangent line to kA k_A in A and tB t_B the tangent line to kB k_B in B. Let P P be the point of intersection of tA t_A and tB t_B. Given are the points A A and B B. Determine the set of points P\equal{}P(C ) over all points C C, so that ABC ABC is a non isosceles, acute-angled triangle.